The County Registers, which were published by the California State Mining Bureau between 1898 and 1905, contain maps and text on mines in 21 counties of the state. These registers show locations and tabulated data for many historic and operating quartz, placer, drift, and hydraulic mines. They also include lists of mills, arrastras, and mineral springs. The text on quartz mines, for example, includes in tabular form:
- Map location number
- Name of mine
- Nearest town or Post Office
- Location (Section, Township, Range)
- Patent information
- Vein data: number, width, strike, and dip
- Character of ore
- Hanging wall and foot wall material
- Developments (lineal feet) - shaft, incline, open cut, tunnel, drifts, and depth below outcrop
- Number of stamps in the mill (if any) and power source
- Number of men employed
- Name and address of company, owner, or superintendent
- Remarks about the operation
The maps display the corresponding location numbers from the text. In addition, some registers have economic geologic maps as well as general descriptions of the counties and their mineral resources and mining operations. Some also have maps and text on oil fields and associated wells (Kern, Los Angeles, Santa Barbara).
Also included in this collection are two maps showing the boundaries of forest reserves in Shasta and El Dorado Counties. These were issued by the State Mining Bureau in the same time period, but do not include any text.