Mt. Holly Springs: Agate Nodule Rockhounding in Cumberland County, Pennsylvania

Quick details

Access

Public area

County

Cumberland County

State

Pennsylvania

Nearest road

Cold Springs Road

Postcode

17013

Coordinates

40.10906, -77.23909

Geology at Mt. Holly Springs

This spot sits on Tomstown Formation, mapped as dolostone that formed roughly 540 to 485 million years ago. Chert and agate nodules typically form inside carbonate rock like this and weather out as tough, waxy lumps in soils and creek beds.

Mapped unit

Tomstown Formation

Age

540–485 Ma (Cambrian)

Rock types

dolostone

Elevation

650 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 Mt. Holly Springs

Best months: March to November. Typical highs run 85°F in midsummer and 37°F in midwinter, with winter lows near 20°F.

Climate normals: NOAA 1991-2020 monthlies, CARLISLE WTP station (8 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 Mt. Holly Springs

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

• Agate NoduleEncyclopedia →