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

Updated June 2026

Impassable Rock is a mapped rockhounding spot in Mendocino County, California. Reported finds include rhodochrosite, inesite, bementite, neotocite. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Permission required
County: Mendocino County
State: California
Coordinates: 39.53627, -123.12162

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.

Best time to visit Impassable Rock

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.

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.

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

Found at Impassable Rock

Each chip opens all spots that produce that material; the encyclopedia link opens the full ID and field guide.

Nearby rockhounding spots

Other rockhounding spots within driving distance of Impassable Rock.

Impassable Rock FAQ

Where is Impassable Rock?+

Impassable Rock is in Mendocino County, California, at 39.53627, -123.12162.

What rocks and minerals can you find at Impassable Rock?+

Impassable Rock is reported to produce Rhodochrosite, Inesite, Bementite, Neotocite.

Is collecting allowed at Impassable Rock?+

Permission required before collecting. Requires landowner or agency permission before any collecting. Do not enter without explicit authorization. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Impassable Rock?+

A rock hammer, sturdy gloves, safety glasses, and a collecting bag cover the basics here. Add a spray bottle: wet rock shows color and pattern that dry rock hides.

When is the best time to visit Impassable Rock?+

The most comfortable months at Impassable Rock are February to November.

How do I get to Impassable Rock?+

Open the directions link to navigate to 39.53627, -123.12162 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in California

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Open Impassable Rock on the map

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