Impassable Rock: Rhodochrosite & Inesite Rockhounding in Mendocino County, California

Plan your visit

Permission required before collecting

County

Mendocino County

State

California

Coordinates

39.53627, -123.12162

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Permission required before collecting

Requires landowner or agency permission before any collecting. Do not enter without explicit authorization.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Best time to visit Impassable Rock

Comfortable months (45 to 90°F highs)

Best months: February to November. Typical highs run 80°F in midsummer and 42°F in midwinter, with winter lows near 20°F.

Climate normals: NOAA 1991-2020 monthlies, POTTER VALLEY POWERHOUSE station (12 mi away), adjusted for elevation.

Geology at Impassable Rock

This spot sits on Franciscan schist, mapped as mica schist that formed roughly 145 to 100 million years ago. Metamorphic rock like this weathers into resistant float, and minerals that survive transport typically concentrate in nearby drainages.

Mapped unit

Franciscan schist

Age

145–100 Ma (Early Cretaceous)

Rock types

mica schist

Elevation

5,630 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

State guidance last verified: April 1, 2026

• BLM California, Recreational mineral collecting
• California Geological Survey
• CDFW, Suction Dredge Mining Permit Program
• Community submissions reviewed against published agency rules