Colorado River: Agate & Chalcedony Rockhounding in Grand County, Utah

Plan your visit

Generally open to casual rockhounding

County

Grand County

State

Utah

Nearest road

Dinosaur Diamond Prehistoric Highway

Postcode

84532

Coordinates

38.60268, -109.58412

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 Colorado River

Comfortable months (45 to 90°F highs)

Best months: February to May. Typical highs run 99°F in midsummer and 42°F in midwinter, with winter lows near 23°F. Monsoon storms peak in July and August and can flood washes fast.

Climate normals: NOAA 1991-2020 monthlies, ARCHES NP HQS station (2 mi away).

Geology at Colorado River

This spot sits on ground mapped as Stream alluvium that formed within roughly the last 129,000 years. Petrified wood typically travels as tough float, and worked gravels like these are exactly where weathered pieces tend to collect.

Mapped unit

Stream alluvium

Age

< 1 Ma (Late Pleistocene to Holocene)

Elevation

3,970 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 Utah, Rockhounding overview
• Utah Geological Survey, collecting guidelines
• SITLA, surface use rules
• Community submissions reviewed against published agency rules