Mattawa: Opalized Wood Rockhounding in Grant County, Washington

Updated June 2026

Mattawa 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
Coordinates: 46.77474, -119.84886

Geology at Mattawa

This spot sits on Asotin Member, Saddle Mountains Basalt, mapped as basalt flows (asotin member [crb and smb]) 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: Asotin Member, Saddle Mountains Basalt
Age: 23–5 Ma (Miocene)
Rock types: basalt flows (asotin member [crb and smb])
Elevation: 1,390 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 Mattawa

Best months: March to November. Typical highs run 88°F in midsummer and 37°F in midwinter, with winter lows near 26°F.

Climate normals: NOAA 1991-2020 monthlies, PRIEST RAPIDS DAM station (9 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 Mattawa

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 Mattawa.

Mattawa FAQ

Where is Mattawa?+

Mattawa is in Grant County, Washington, at 46.77474, -119.84886.

What rocks and minerals can you find at Mattawa?+

Mattawa is reported to produce Opalized Wood.

Is collecting allowed at Mattawa?+

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 Mattawa?+

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 Mattawa?+

The most comfortable months at Mattawa are March to November.

How do I get to Mattawa?+

Open the directions link to navigate to 46.77474, -119.84886 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in Washington

See all 92 Washington spots →

Open Mattawa on the map

Use the RockHoundR app for live land overlays, weather, geology, directions, and saved finds.