Santa Cruz County History - Making a Living



Over-Gear Wheel Mill #2
by Barry Brown

Photograph of the Over-Gear Wheel Mll #2
The Over-Gear Wheel Mill #2
Photograph from the Museum of Art & History @
The McPherson Center, Santa Cruz, CA

This cavernous concrete structure was the #2 Wheel Mill, one of 10 created to combine the ingredients which made gun and blasting powder. This process, called incorporation, was accomplished by amalgamating a mixture of 75% saltpeter (potassium nitrate), 12.5% charcoal, and 12.5% sulfur under a pair of seven-ton cast-iron wheels rotating in a castiron pan from four to eight hours depending on the quality and type of powder required. The roofs and doors of the Wheel Mills were designed to give way in case of an explosion and the massive concrete walls directed the blast up and away from the other Mills.

The men were not allowed to wear shoes with metal in their soles and all the equipment they used had to be made of non-ferrous materials such as wood or copper. They were responsible for measuring and mixing the ingredients as well as keeping the mixture damp. Because the wheels and pan were made of cast-iron, the men’s most important task was to maintain a sufficient amount of the damp mixture between the wheels and the pan to avoid sparks. This was what made this process so inherently dangerous. The product they made here was a granular mass called Mill Cake.

Photograph of Wheel Mll Destroyed in an Explosion
Wheel Mll Destroyed in an Explosion
Photograph Courtesy of Special Collections,
UC Santa Cruz, Santa Cruz, CA

Over the years, there were many explosions in the Wheel Mills; some were lethal, all were destructive (see picture to right). Wheel Mill #2 is the last of the original ten Mills left as abandoned. Once the CPW ceased operations in Santa Cruz, all scrap metal at the Powder Works, including the big wheels, was removed to the California Powder Works' Hercules Plant in Pinole California on the San Francisco Bay.


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View similarly tagged articles:

dynamite, powder works, San Lorenzo River

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