General Area: Moss Agate & Plume Agate Rockhounding in Brewster County, Texas

Plan your visit

Generally open to casual rockhounding

County

Brewster County

State

Texas

Nearest road

Calamity Creek Road

Coordinates

30.16759, -103.59482

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

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.

Best time to visit General Area

Comfortable months (45 to 90°F highs)

Best months: July to May. Typical highs run 89°F in midsummer and 59°F in midwinter, with winter lows near 30°F.

Climate normals: NOAA 1991-2020 monthlies, ALPINE station (15 mi away), adjusted for elevation.

Geology at General Area

This spot sits on Duff Formation (with Decie Member from Paisano caldera shown separately), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided, mapped as rhyolite that formed roughly 38 to 28 million years ago. Volcanic ground like this is where agate, jasper, and other chalcedony typically form, filling old gas pockets and fracture seams in the flow rock.

Mapped unit

Duff Formation (with Decie Member from Paisano caldera shown separately), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided

Age

38–28 Ma (Late Eocene to Early Oligocene)

Rock types

rhyolite

Elevation

4,920 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

• Texas Parks and Wildlife Department
• Bureau of Economic Geology, Texas geology
• Big Bend National Park, Rules
• Community submissions reviewed against published agency rules