White Marsh: Amethyst Rockhounding in Baltimore County, Maryland

Quick details

Access

Public area

County

Baltimore County

State

Maryland

Nearest road

Red Trail

Postcode

21128

Coordinates

39.38832, -76.44688

Geology at White Marsh

This spot sits on Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation, mapped as sand that formed roughly 145 to 66 million years ago. Loose deposits like these are float-collecting ground: erosion keeps moving durable rocks and minerals into gravel bars, cutbanks, and washes.

Mapped unit

Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation

Age

145–66 Ma (Cretaceous)

Rock types

sand

Elevation

100 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.

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 White Marsh

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

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