Blanco Trading Post: Chalcedony Rockhounding in San Juan County, New Mexico

Quick details

Access

Public area

County

San Juan County

State

New Mexico

Nearest road

State Highway 57

Postcode

87418

Coordinates

36.34672, -107.82529

Geology at Blanco Trading Post

This spot sits on Nacimiento Formation, mapped as sandstone, shale, and conglomerate that formed roughly 66 to 56 million years ago. Tough silica like agate, jasper, and chert typically weathers out of beds like these and collects as float in drainages and on deflation surfaces.

Mapped unit

Nacimiento Formation

Age

66–56 Ma (Paleocene)

Rock types

sandstone, shale, and conglomerate

Elevation

6,850 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 Blanco Trading Post

Best months: February to November. Typical highs run 88°F in midsummer and 40°F in midwinter, with winter lows near 19°F.

Climate normals: NOAA 1991-2020 monthlies, OTIS station (1 mi away).

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

• Rockhound State Park — Collection rules
• BLM New Mexico
• New Mexico Bureau of Geology and Mineral Resources
• Community submissions reviewed against published agency rules

Found at Blanco Trading Post

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

• ChalcedonyEncyclopedia →