Monthly Archives: January 2014

Sonoma Magnesite Mill

The Sonoma Magnesite Mill is shown in this photo mid way through its useful life.  Click photo for a more detailed image.


The detailed image has various locations in the main building and the right lean-to labeled.  The lean to at the front of the building was an addition after the main building was constructed in order to accommodate a second rotary kiln.  When the second rotary kiln was added, some of the equipment needed to be moved out of the way, necessitating the lean-to.  This series of photos shows the evolution of the mill.

This first photo dates to October 9, 1915 when it was printed in the Guerneville Times.  Photo provided courtesy of John C. Schubert.  Annotations on these photos are mine and are the best judgements on what individual components of the photos represent.  The first photo is just prior to beginning production or shortly after production began.  Note that the siding on the front wall is not complete.  I suspect it was left open to allow the rotary kiln and other equipment to be brought into the building.  The kiln is installed at this point as evidenced by the stack protruding from the top right of the rear gable of the roof.  Click the photo for a larger image.


This image is from a August 25, 1917 U.S. Geological survey.  It is a cropped and more detailed version of the first image.  I believe this is a construction photo of additions being made to accommodate a second rotary kiln.  It hasn’t been installed as there are only two large smoke stacks protruding from the roof.  I believe the right crushing area no longer has its exterior siding as it is being prepped for dismantling.  Addition of a second kiln would have bumped plant capacity to 60 tons a day.  It is likely that required an upgrade in the rough crushing capacity on the right side of the mill.

The shed on the front housed an interior siding for loading calcined ore on flat cars along with the fine crushing equipment.  The shed was needed in order to move equipment off the floor of the main structure to make room for the second kiln.  Click the picture for a more detailed image.


This the and fourth photos were taken in November 1923.  The third is from the collection of Jane Barry and the fourth from the collection of Hart Corbett and was provided courtesy of John C. Schubert.  The photographer is facing the left side of the building as viewed from the front.  The second kiln is clearly installed in this photo as evidenced by the stack on the front gable of the main building and the oil tank feeding the kiln through the wall.


The fourth photo was taken about the same time.  This image shows the siding that was constructed entering the front shed addition which provided a covered space to load calcined ore bags and barrels.  I believe the fine crushing equipment was also located in this room.  The other notable change is the timber structure to the right of the building which replaced the rough finishing shed in photos one and two.  This structure would have housed a large rough crusher like a Blake crusher.  The timber structure would have expanded the hopper capacity of the crusher, elevated it off the ground and probably also housed screening equipment that separated ore crushed to 2″ or less from oversized ore.  The ore passing the screen would have been routed to the kiln for calcination.  That failing the screen would have been run back through the crusher.  Click on the photo for a larger image.


This is the sole interior shot of the main building.  The shot looks down the interior rear gable taken from the left side of the building.  This shot is most likely to have been taken prior to installation of the second kiln.


The original kiln was located along the back wall of the main building  That means the front half of the building was initially available for other equipment involved in ore processing.

Lets see if we can figure out dimensions and materials for the structures.  I’ll rationalize assumptions as to dimensions.

Main Structure

Length – 70 feet in 1:1 scale.  The rotating kiln is 50′ long.  Both the cooling on the left side would have occurred in the main structure.  The fine crushing probably occurred in the left lean-to shed after the calcined ore had cooled.  The rough crushing on the right side apparently initially occurred under a lean-to shed in the earliest photo.  Later, the right lean-to was replaced with a timber crushing tower.

Width – 30 feet in 1:1 scale.  The kiln appears to take roughly 50% of the space on the back side of the building.

Wall Height – The top of the kiln hopper is even with the side wall.  If you look at the earliest photo above, a man appears to be pushing a wheel barrel along side the building.  From his size, I’m estimating the exterior doors to be 8′ high.  They would have been a minimum of 6’8″  That would have put the side walls at roughly 16′, a fairly standard dimension in construction.

Roof Pitch and Height – The roof pitch appears to be around 4:12, 4′ of rise for every 12′ of run,  That would make the peak 5′ above the side walls or 21′ off the ground.

Framing Timber – Side wall studs appear to be 4′ on center, possibly made from 3″ x 6″ timber.  Construction is much like a common pole barn today.  I suspect the wall lateral pieces are 2″ x 6″ nailed to the outside of the vertical timber, and are spaced every 4 feet vertically.

Roof Trusses – Are also spaced every 4′.  The laterial cords are probably made from 2″ x 8″ lumber.  The rafter portion would have been made from the same material.  A vertical cord supports the middle of the truss spans.  A diagonal support stretcher hits each vertical framing timber about 5′ from the ceiling and the lateral cords about 1/4 the way across the span.  I’m assuming the trusses are mirrored on the front side of the building.

Celestory – There is a celestory along the peak of the roof.  Presumably the purpose was to allow hot air and dust to be expelled.  It appears as though venting is supplied with sheet metal grates.

Wall coverings – are clearly ribbed metail siding.  It looks as though the same material was used on the roof.  The top 2′ appears to be made of a semi-transparent material that admits light.

Floor – I suspect the floor was made up of wood boards supported by wood beams. I suspect 2″x8″ flooring.  In the area underneath the kiln, the boards are protected from fire with two layers of brick.  While there probably wasn’t a basement, some provision will need to be made for transferring cooled calcined ore to the fine crusher for crushing.

Fine Crushing Lean-to Shed

If you look at the photos the left lean to extends more than 1/2 the depth of the structure.  It looks to be roughly square.  I’m estimating its dimensions to be 18′ by 18′.

Wall heights on the outside end would be 12′ increasing to 16′ by the time the roof intersected with the main structure.

Power House

It is hard to estimate the depth of the power house from the photos but I suspect it extended to the rear of the building.  Given the front lean-to is 18′ deep, the power house would have been 12′ deep.  The length appears to match the front lean-to so would be 18′

The shed roof appears to meet the main building just under its roof line so height at the rear of the power house would be just under 16′ with the height on the front side just under the main structure roof at the 12′ point.

Note that in the later photos a small shed has been added to the power house presumably to add to its capabilities.  That shed would appear to be 12′ by 12′ with a roof on the low end of 9′ rising to 10′ on the high end.

Rough Crushing Lean-To Shed

This shed appears on the right side of earliest two photos.  It appears to be similar in size to the fine crushing shed on the left with a similar roof line.  Fine crushing shed dimensions were estimated at 18′ by 18′.  Wall heights on the outside end were estimated to be 12′ increasing to 16′ by the time the roof intersected with the main structure.  Note that this shed was dismantled and replaced with a timber structure containing a larger crusher about the time the second rotary kiln was installed.

Timber Rough Crushing Structure

This structure appears in the last photo and is likely to have contained a large Blake Crusher and screening used to separate crushed ore that passed a 2″ screen.  Crushed ore passing the screen went to the kiln for calcinating.  Crushed ore that didn’t pass the screen was routed back to the crusher for crushing.  This appears to be a roofed structure with the top sides open as the hill can be seen through that portion go the structure.


Height appears to be close to the roof of the main structure plus the celestory or roughly 23′.  The top of the side walls up to the opening would be roughly 19′.  Timber braces are likely to be 4″x8″ or there about.  There are 5 timber braces per side and the structure appears to be roughly square.  Diagonal braces uses to prevent racking are  likely to be 2″ x 8″.

Hopper wall boards are also likely to be 2″x8″.  It is likely the hopper boards extend roughly 1/2 way down the structure.  The structure below the hopper boards appears to be somewhat open.  I suspect the 2″ screen would have been mounted diagonally with material failing the screen dropping off to the rear of the structure.  That passing through the screen would fall to a ramp mounted at a diagonal with the ore passing the screen dropping off in the direction of the rotary kiln.

I would estimate structure dimensions as 12′ x 12′.


My current inclination is to model the mill with the additions that occurred in around 1917 to 1918 (final mill image).  I’ll model with both kilns to deal with the production driven by World War I and an additional ore discovery.  I’m going to assume the timber rough crusher had arrived and was installed.

In order to display what is occurring inside, the main roof will be removable along with the roof to the power house and to the fine crushing area.  Sliding doors on the front shed addition will be modeled open for additional viewing.

Builders logs for construction of component parts of this mill setting will appear just below as the projects are activated.


Rotary Kiln Supports

Rotary Kiln Lg

The Sonoma Rotary kiln appears to be supported by poured concrete.  In the front of the picture, rails are supported by a poured concrete wall at floor level.  The walls form pits where hot calcined ore drops and cools after being calcined in the kiln.  In some cases, the pits were lined with steel.

The first band, positioned approximately 10′ down the length of the tube is supported on what appears to be a brick floor, one course higher than the poured concrete floor.  The additional brick course plus fact the rollers are larger in diameter than the wheels that run on the rails would allow the kiln to be modeled at a slight angle from a horizontal position.

The second band approximately 40′ down the length of the tube is supported on a poured concrete pier that looks to be about 3′ off the floor.  Taking away the effect of the brick course, the rise would appear to be roughly 1 inch for each foot of run.

The support on the far end includes the chimney and hopper.  See the hopper and chimney page for more details.  It is made up of brick and is high enough to fully surround the rotary kiln tube.

The floor itself appears to be a double layer of brick on top of the wood floor, supported by wood beams.  Presumably, the purpose of the brick is to provide fire protection on the floor in the area of the kiln.


This image shows the kiln tube at the kiln hood end.  The hood will be fabricated from the right piece 1 1/4″ code 40 PVC joiner.  The two tires will be made up of narrow pieces like the piece in the middle.  The rollers that will support the tires are just below the tire in this photo.


Rotary Kiln Hopper and Chimney

The side of the rotary kiln accepting ore crushed to fit through a 2″ screen serves the following functions.

  1. It supports the end of the kiln.
  2. It provides an exhaust for the chimney.
  3. It includes a hopper that allows incoming ore to be loaded into the kiln.

This only photo of the prototype of the hopper and chimney area is not very revealing.

Rotary Kiln Stack1

This is from a 1917 rotary kiln drawing and shows a hopper and support mechanism from the side.



This shot of an early English rotary kiln shows a masonry firebox support with the chimney coming out the top.

Kiln Chimney

A close look at the first photo reveals the fire box feeding the chimney to be also made from masonry.  The end would have been deeper on the Sonoma kiln to allow the hopper to be placed near the top front and the chimney to come out the top rear.   Note that the chimney diameter in this photo appears to be around two feet, but the chimney on the Sonoma kiln is of a smaller diameter, slightly smaller than the hopper tube.

Time to make some executive decisions.

  • The fire box supporting the hopper and chimney will be modeled based on the English kiln in the above photo, except it will be wider to support both the chimney and the hopper.
  • It will be all brick up to the point the chimney and hopper exit the fire box.  Construction will use .060 styrene sheet with Plastruct rough brick applied to the surface.
  • 1:1 dimensions will be 14′ high by 10′ wide by 8′ deep.  That scales to 3 1/2″ x 2 1/2″ x 2″.
  • Both the chimney and the cylindrical portion of the hopper will be 2′ in 1:1 scale or 1/2″ scaled.
  • The kiln will be supported with a PVC ring similar in size to the tires.
  • The fire box will have a fire door similar to that in the above photo except the top will be squared rather than rounded.
  • The rectangular portion of the hopper will be built to accept material from the conveyor on order which scales to 4 1/2″ high.



This is a shot of the styrene piece that will be the wall of the fire box that receives the kiln cylinder.  I used the PVC joiner to scribe a circle that would allow the cylinder to pass through the wall.  Then I drilled 1/8″ holes inside the circumference (mostly) and used an Exacto knife to connect the holes.


The next step is to glue a PVC joiner to the back of this sheet, then use a rat tail file to size and smooth the final opening.  While the epoxy was setting up I moved on to the fire box roof.  Two openings were required, one for the smoke stack and the second for the cylindrical portion of the hopper.  I drilled 1/4″ holes in the roof, used the stack to draw two circles, then used a rat tail file to file the opening so it would accept 1/2″ tube.  As you can see I used a couple of pieces of Plastruct square tube to convince the chimney not to lean.


This shot shows progress in the fire box, hopper and chimney area.  In addition to the top of the firebox supporting the chimney and tube portion of the hopper, the firebox wall facing the tube is also shown.  As you can see it is designed to support the cylinder at a downward slant from where it enters the fire box.  You can also see the three other sides and the bottom of the fire box.  The firebox will be surfaced with Plastruck brick which is on order.  The brick will come most of the way up the fire box.  The last portion will be modeled as a steel hood.


PC&N Mini Layout Structures

When I designed this layout, I figured I’d be limited to face structures that could rest on the small 1×2″ moulding at the top of my car siding knee walls.  Of course more of these structures (including docks) would protrude more than 1 1/2 inches from the drywall.  This in turn creates a bit of a problem when the shelf is rotated into vertical position as the portion of the shelf against the wall actually rotates up 1/4 to 1/2 inch.

Then I saw a post in another forum inciting that many modelers do not fix their structures in place on top of the benchwork surface.  They float them so they can pick them up if they need or want to.  Seams are covered with clutter, weeds, ballast, etc.That would solve my problem as long as I had a place to put them when removed from the layout.  A shelf directly above would fill that need.

So I’m going to experiment with removable structures.   Aside with dealing with the issues with face structures, this approach would also allow me to put some structures on the layout surface itself.

PC&N Picnic Car

The North Pacific Coast transported folks wanting to get away from San Francisco for the weekend North to a number of locations along the Russian River in open Picnic Cars.  The following photo shows a Picnic Car in the Sausalito docks area in the 1890s.


The picnic car is the last car in the rightmost consist in the above photo.


A picnic train is caught leaving Cazadero in the above photo.

One of the restoration societies has taken one of its 1:1 Carter flats and is converting it into a picnic car.  The following photos show the car mid-construction.



I think I’ll do the same thing in adding some picnic car interest to my layout.

Rotary Kiln End Hood Log

I’m estimating the end hood to be 3 feet deep in 1:1 scale or 0.75″ in 1:48.  This will be modeled using a slice of the joiners for 1 1/4″ code 40 PVC.  A scction will be cut from a portion of the bottom of the PVC piece to allow the brick to extend below the outer diameter of the joiner to model the dumping of calcined ore into the steel lined concrete bunker below the kiln.  A close look at the band surrounding the brick on the left side reveals that the brisk is recessed somewhat from the end using an L girder formed to the curve of the end hood.  The best approach may be to wrap the PVC joiner slice in brass or styrene to form the overlap then place a brass or styrene ring vertically against the brick and horizontally from the inside against the wrapping.


The Crowe River order includes some brick sheet that should cover what I need on the lower end of the tube as well as the base for the chimney at the upper end.


I’ll need to locate suitable boiler doors for the hood and fabricate the piping for the oil line feeding the burner.  The support trucks on the two sides and the rail construction are being logged in the Rails, Wheels and Rollers Log.

Rotary Kiln Electric Motor & Gears Log

This log will document modeling of the electrical motor and gears driving rotation of the cylinder of the rotary kiln.

The drive gear in all likelyhood was electrically driven.  I’m hoping this Crow River motor is appropriately sized.


In at least one rotary kiln installation I observed the use of bevel gears.  So I ordered these from Crow River.


The most vexing problem related to the kiln tube was locating a scaled version of the large gear surrounding the rotary kiln cylinder.  Then I stumbled on a Spirograph set containing a wide variety of gear sizes.  I purchased the kit hoping one is of the ideal size for this application.  I’m going to keep my fingers crossed on this one.  Additional work on the tube will need to wait until the Spirograph gears arrive.  One of these should be large enough to go around the rotary kiln tube.  Another should be small enough to serve as the final output gear from the electrical motor.  Gear tooth density is appripriate for this model and the gears will mesh – that’s what Spirographs do.




The Spirograph arrived.  It turned out that the 84 tooth gear accepts Code 40 PCV Joints perfectly.  So I cut two very thin pieces and epoxied them to the Spirograph gear, sandwiching it between.  When the sandwich dried, I used my drill press to drill holes around the inside edge of the PVC joint slices.  After connecting the dots. I used the Exacto to trim the gear flush with the inside of the joiner, allowing my gear mechanism to slide on the tube as shown on this photo.



Immediately below the gear on the tube is the electric motor I ordered from Crow River Products to power the rotation of the tube.  The motor is sufficiently beefy that it is credible in this application.  The light colored plastic gear is the 24 tooth gear from the Spirograph set.  which will be used to transmit power from the motor to the large gear surrounding the kiln.  I also show a pair of beveled gears I ordered from Crow.  I need to work on the arrangement of the gear box.

Rotary Kiln Rails, Wheels & Rollers Log

This log will document modeling of the rotary kiln rails, wheels, and rollers pictured further down this post.

If you look at the earlier photo of the rotary kiln, you will see the front shroud is supported by freight car wheels on rails.  I intend to model the support brackets with styrene, the rails with scrap rails, and the wheels with sourced freight wheels.  A rough estimate of 1:1 diameter would be 18″.


I also plan to model the support brackets for the rollers supporting the tyres from styrene.  The wheels will probably be modeled using appropriately sized pulleys.  A rough estimate of 1:1 diameter would be 24″.


This drawing of tire assembly design shows common British practice in the early 1900s.


With these two applications in mind, I picked up these 33″ HO wheels off eBay.  At 1:1, they should be about 1/3 inch in diameter.  Any left will be used as clutter, probably in the Sausalito Shops scene.

33 inch HO Wheels

I also ordered Crow River Products 24″ pulleys to be used as rollers for the tires.



The 24″ pulleys arrived.  They are a very close match to the rollers that supported the prototype tires as shown in this photo.


Rotary Kiln Tube & Tires Log

Rotary Kiln

This log will document modeling the rotary kiln 50′ long tube and tires pictured in the above photo.

1 1/4 inch code 40 PVC has an outside diameter of 1.66 inches, just a hair short of the diameter in the above takeoffs.  The connectors that join two lengths are 1.97 inches, also a hair short of the diameter of the tires in the above takeoffs.  I picked up a 2′ length of 1 1/4 inch code 40 at Home Depot along with three connectors.


I cut the 1 1/4″ PVC to 12.5″ (50′ in 1:1 scale) with my chop saw and cut the remaining piece in half, fitting the connectors on each end.  Then I sliced off a number of sections of the connectors.  From the bands on the tube I will select:

  • One will hold the tube on the kiln hood end.  I’m estimating the with of this piece to be 3′ at 1:1 scale, or 3/4″ in 1:48.  That is the size of the longest slice on the tube.  It is slanted slightly to counterbalance the fact the tube will be mounted at a slight angle to horizontal.
  • Another will be hidden behind the hopper on the far end and serve as a bearing for that end.   Width may be somewhat immaterial as it will be hidden inside the hopper.  Of the four medium length slices shown I’ll pick one and sand to a slight angle to allow the end to stand vertically even though the tube will be slanted.
  •  I’ll pick the best two of the three narrow bands and sand appropriately so they can serve as tires.


I plan to make use of a trick I learned from David Fletcher for putting rivets on boilers.  If I wrap the tube with thin brass sheet or thin styrene, I can press rivets in the sheet with my drill press from behind the sheet. Final alignment of these parts will be somewhat dependent on the solution used to handle the large gear surrounding the tube.  So much of the work on this part of the kiln will need to be suspended until my gear source, the Spirograph, arrives.


Sonoma Ore Processing

The following quote describes the processing of magnesite ore at the Rose Fire Brick Company in Oakland, California using production from the Red Mountain Magnesite Mine, the largest Magnesite mine in the US in 1905.  The quote is quite relevant in that it describes the entire ore processing process from the mine through the delivery of the finished product.

“Raw magnesite was shipped by wagons from the Red Mountain mine to the Livermore depot and then loaded into the cars of the Southern Pacific Railroad Company. The cars were transported to the Rose Firebrick plant, where they were pushed up an incline so that the magnesite ore could be dumped into bins. The magnesite was ground into granules in the crusher and raised in automatic elevators to the higher end of the rotary kiln. As the magnesite granules passed through the rotary kiln, they were calcined, whereby carbon dioxide was driven off by high temperatures (2,800 degrees F) to reduce the ore to a dead-burned magnesia, or fine pure crystals of periclase (magnesium oxide). Carbon dioxide was collected and sent to the Pacific carbonic gas plant to be converted into a liquid product. In the pug mill, the periclase was mixed with a little water, a pinch of crushed quartz, and not more than 10 percent iron. This mixture was then sent to the molding room to be power pressed into bricks and then sent to the dryer to drive off any remaining water. After drying, the bricks were fired at a high temperature in the rectangular kiln. The finished magnesite brick was shipped locally by rail and by ship to New York for use in the open hearth furnaces of steel mills.”

It is clear from the photos that plant production at the Sonoma Magnesite plant was not fire bricks.  Rather it was likely to be magnesium oxide crystals that were transported from the plant in canvas bags or metal drums for processing into magnesite bricks by the firm buying the powder shipped in the bags in this photo of a consist from the Sonoma Magnesite Company plant.


But in a much less sophisticated sense, the Sonoma plant and the mines would require a similar process to the Rose Fire Brick company with the exception the powder wasn’t turned into bricks.  Here’s my best guess on how that process worked at the Sonoma Magnesite mine and plant.

This quote in “Mines and mineral resources of the counties of Colusa, Glenn, Lake, Marin …” by Walter Wadsworth Bradley, California State Mining Bureau explains the process at the Sonoma plant.

“The magnesite is being mined at the lower (Cecilia) deposit, where a quarry face has been opened up.  In the calcining plant, a rotary kiln, oil fired, is in operation with a capacity of 30 tons in 24 hours.   A second kiln is stated to be in route for installation.  The crude material is crushed to pass a 2 inch ring, before charging to the kiln: and the calcined material is crushed after cooling in steel bins.  Power is obtained by an oil burning steam plant.  The kiln consumes 3/4 barrel of oil per ton of calcined magnesia obtained which is reduced to 5% CO2.  The finished product is packed in paper lined duck bags for Pacific Coast consumption, and in 400 pound paper lined barrels for the eastern market.  Shipments are now being made via the Panama Canal to New York, an ocean rate of $5 per ton from Tidewater, San Francisco to New York having been obtained.  Seventy men are at work. – W.W.B – July, 1915.”

The process in a modern Magnesite ore crushing plant works like this.


In the 1910s it might have worked like this:

  • The mines in all likelihood used dynamite to break up the magnesite ore into rocks which were transported by gondola to the plant.

  • The ore was sorted, crushed and screened into rocks 2″ in diameter or less.Magnesite_Ore
  • The crushed rock was fed into the rotary kiln for processing.  After being processed and cooled, the calcined ore was crushed into powder.magnasite-powder-500x500
  • Fire bricks were created in San Francisco or New York by the firm receiving the powder.  This is a fire brick produced by the Rose Fire Brick Company in San Francisco, one of the firms that might have been receiving the bags of ore powder.images-2

The following photo is of the Sonoma Magnesite Company Mill located in the area of the mines.


The lean to shed at the left of the photo is likely to be where initial ore crushing into screened rock 2″ or less in diameter occurred.  You can see a hopper protruding from the top of the shed.  It appears the man in the photo may be loading ore from the pole nearer the lean to into the bottom end of the hopper.

The shed at the front of the photo was built when a second rotary kiln was added, presumably to house equipment that had been located in the front gable of the original mill structure.  In modeling the mill, I’m tempted to leave the front lean to off, modeling the mill in its original state.  Doing so would allow me to open the near side of the main building so the rotary kiln and related equipment for viewing.

A commonly used rock crusher in the era was the Blake Crusher.  The following image shows how it works.  The Blake would have been the crusher under the shed to the right of the main building loaded with the hopper.


This is a photo of a Blake Crusher in the era being modeled.


Blake crushers came in a variety of sizes as shown by this photo.  Note the man in the photo.


Blake crushers were initially powered by belt driven by steam engines as indicated in this drawing.


This photo shows a Blake Jaw Crusher encased in a timber structure designed to elevate the crusher and extend the size of the bin accepting incoming ore.  Directly in ffont of the crusher is a stationary steam engine that was presumably used to power the crusher.  Note the bucket system on the left that was used to lift the ore into the hopper.


This is an image of a typical magnesite processing plant.  The rotary kilns are in the middle of the structure.  I believe the large timber structure on the left contains a Blake crusher.  The timber structure on the right would contain post processing equipment.


I suspect the ore came into the Sonoma Magnesite plant from the right via gondola on the spur that turns to the right on the above plant photo.  Once crushed, a conveyer (steam driven) would lift the crushed ore into the input end of the rotary kiln.  The the rotary kiln output of calcined ore would have dropped into the steel bins shown in the rotary kiln photo where they would have cooled.

Once the ore had cooled it would be crushed into powder.  A common machine for crushing ore into powder was the Sturtevant Ring Roll Mill.  They were delivered as single mills or as duplex mills.  A duplex mill is shown in the middle right of the following image.  Cement and Engineering News #31 indicates the capacity of their No.2 Duplex Mill was 16 to 20 tons per hour at 20 mesh (20 mesh openings per inch) and 8 to 14 tons per hour at 80 mesh.  A single No 2 Duplex mill would have been adequate to handle output from the two kilns of 60 ton per day input, 45 ton output in an 8 hour shift.

Sturtevant Crusher

Once the calcined ore had been crushed into powder, it would have been bagged or poured into drums then transported via flat car to the Cazadero area where it would interchange with the narrow gauge.