Grand Coulee: Opalized Wood Rockhounding in Grant County, Washington

Updated June 2026

Grand Coulee is a mapped rockhounding spot in Grant County, Washington. Reported finds include opalized wood. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Grant County
State: Washington
Nearest road: Alcan Road Northeast
Postcode: 99133
Coordinates: 47.92966, -119.00715

Geology at Grand Coulee

This spot sits on Grande Ronde Basalt, N2 (CRB), mapped as basalt flows (granderondebasalt and upper flows of norm.mag.pol.) that formed roughly 23 to 5 million years ago. Petrified wood typically comes from volcanic ash beds like the ones associated with this ground, where buried forests were slowly replaced by silica.

Mapped unit: Grande Ronde Basalt, N2 (CRB)
Age: 23–5 Ma (Miocene)
Rock types: basalt flows (granderondebasalt and upper flows of norm.mag.pol.)
Elevation: 1,960 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 Grand Coulee

Best months: March to October. Typical highs run 87°F in midsummer and 32°F in midwinter, with winter lows near 22°F.

Climate normals: NOAA 1991-2020 monthlies, COULEE DAM 1 SW station (2 mi away), adjusted for elevation.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

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

Washington Geological Survey (DNR)
Stonerose Interpretive Center — Visit & rules
BLM Spokane District
Community submissions reviewed against published agency rules

Found at Grand Coulee

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

Opalized Wood Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Grand Coulee.

Grand Coulee FAQ

Where is Grand Coulee?+

Grand Coulee is in Grant County, Washington, at 47.92966, -119.00715. Nearest road: Alcan Road Northeast.

What rocks and minerals can you find at Grand Coulee?+

Grand Coulee is reported to produce Opalized Wood.

Is collecting allowed at Grand Coulee?+

Generally open to casual rockhounding. Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Grand Coulee?+

A rock hammer, sturdy gloves, and a padded bag cover petrified wood hunting. Most pieces are surface float, so walking slopes and washes beats digging.

When is the best time to visit Grand Coulee?+

The most comfortable months at Grand Coulee are March to October.

How do I get to Grand Coulee?+

Open the directions link to navigate to 47.92966, -119.00715 in Google Maps. The nearest road is Alcan Road Northeast.

More rockhounding in Washington

See all 92 Washington spots →

Open Grand Coulee on the map

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