Buffalo Gap: Fairfield Agate Rockhounding in Custer County, South Dakota

Updated June 2026

Buffalo Gap is a mapped rockhounding spot in Custer County, South Dakota. Reported finds include fairfield agate. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Custer County
State: South Dakota
Coordinates: 43.48871, -103.43419

Geology at Buffalo Gap

This spot sits on Morrison Formation, Unkpapa Sandstone, Sundance Formation, and Gypsum Springs Formation, mapped as sandstone, siltstone, and claystone that formed roughly 175 to 145 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: Morrison Formation, Unkpapa Sandstone, Sundance Formation, and Gypsum Springs Formation
Age: 175–145 Ma (Middle Jurassic to Late Jurassic)
Rock types: sandstone, siltstone, and claystone
Elevation: 3,930 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 Buffalo Gap

Best months: March to November. Typical highs run 87°F in midsummer and 39°F in midwinter, with winter lows near 13°F.

Climate normals: NOAA 1991-2020 monthlies, HOT SPRINGS station (4 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.

Sources: RockHoundR public spot dataset, app land overlays, and local agency review before each trip.

Found at Buffalo Gap

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

Fairfield Agate Encyclopedia →

Nearby rockhounding spots

Other rockhounding spots within driving distance of Buffalo Gap.

Across the state line from Buffalo Gap

Buffalo Gap is close enough to the South Dakota border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Buffalo Gap FAQ

Where is Buffalo Gap?+

Buffalo Gap is in Custer County, South Dakota, at 43.48871, -103.43419.

What rocks and minerals can you find at Buffalo Gap?+

Buffalo Gap is reported to produce Fairfield Agate.

Is collecting allowed at Buffalo Gap?+

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 Buffalo Gap?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Buffalo Gap?+

The most comfortable months at Buffalo Gap are March to November.

How do I get to Buffalo Gap?+

Open the directions link to navigate to 43.48871, -103.43419 in Google Maps. Some spots are remote, so check road conditions before driving out.

More rockhounding in South Dakota

See all 43 South Dakota spots →

Open Buffalo Gap on the map

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