Rockhounding in Sonoma County, California

Sketch map

Woof’s favorite find

Sonoma Mine (Mount Jackson, Great Eastern, and Roaring Lion)

We picked it because its USGS record mentions 2 gem or collectible minerals (Quartz, Agate) and 4 of our card minerals overall. No other named site here scores as high on both counts. USGS lists it as past producer for Mercury. Minerals mentioned: Quartz, Agate, Magnetite, Pyrite. Approx. location 38.544, -122.980. USGS record.

Ask first: a USGS record doesn’t mean you can visit. Find out who owns the land and get permission before collecting.

Field cards: what kind of sites?

Status terms come from USGS MRDS records.

Mineral cards

• Copper

  Mohs 2.5–3. Native copper is soft and turns green as it weathers. Mindat

  20 sites

• Quartz

  Mohs 7. Six-sided points; smoky quartz is NH’s state gem. Mindat

  9 sites

• Pyrite

  Mohs 6–6.5. Brassy “fool’s gold,” often cubic. Mindat

  7 sites

• Gold

  Mohs 2.5–3. Soft, heavy and bright yellow; it doesn’t tarnish. Mindat

  4 sites

• Agate

  Mohs 6.5–7. Banded, translucent chalcedony. Mindat

  3 sites

• Garnet

  Mohs 6.5–7.5. Usually deep red, round many-faced crystals. Mindat

  1 site

• Magnetite

  Mohs 5.5–6.5. Black and strongly magnetic. Mindat

  1 site

Counts are sites whose USGS record mentions the mineral or commodity. Hardness from Mindat.

How we built this page: we counted named sites in the USGS Mineral Resources Data System (MRDS) for this area, left out sand, gravel, crushed stone, clay pits and unnamed sites, grouped them by Census county, and linked every site to its USGS record. We did not visit these sites, and MRDS does not tell you who owns the land or whether collecting is allowed.

Source: USGS Mineral Resources Data System (MRDS). USGS ceased systematic updates to MRDS around 2011, so status and details may be out of date. Each site links to its USGS record.

Updated October 2026