Grubb Lake and Mud Lake: Geode Digging in Lancaster County, Pennsylvania

Updated June 2026

Grubb Lake and Mud Lake is a mapped rockhounding spot in Lancaster County, Pennsylvania. Reported finds include geode, limonite. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Lancaster County
State: Pennsylvania
Nearest road: Ironville Pike
Postcode: 17512
Coordinates: 40.06010, -76.44938

Geology at Grubb Lake and Mud Lake

This spot sits on Ledger Formation, mapped as dolostone that formed roughly 540 to 485 million years ago. Limestone country like this is classic geode ground: cavities in the carbonate rock can line themselves with quartz or calcite crystals.

Mapped unit: Ledger Formation
Age: 540–485 Ma (Cambrian)
Rock types: dolostone
Elevation: 480 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 Grubb Lake and Mud Lake

Best months: March to November. Typical highs run 84°F in midsummer and 37°F in midwinter, with winter lows near 19°F.

Climate normals: NOAA 1991-2020 monthlies, LANDISVILLE 2 NW station (4 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.

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

Found at Grubb Lake and Mud Lake

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

Nearby rockhounding spots

Other rockhounding spots within driving distance of Grubb Lake and Mud Lake.

Across the state line from Grubb Lake and Mud Lake

Grubb Lake and Mud Lake is close enough to the Pennsylvania border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Grubb Lake and Mud Lake FAQ

Where is Grubb Lake and Mud Lake?+

Grubb Lake and Mud Lake is in Lancaster County, Pennsylvania, at 40.06010, -76.44938. Nearest road: Ironville Pike.

What rocks and minerals can you find at Grubb Lake and Mud Lake?+

Grubb Lake and Mud Lake is reported to produce Geode, Limonite.

Is collecting allowed at Grubb Lake and Mud Lake?+

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 Grubb Lake and Mud Lake?+

Bring a crack hammer, a chisel, safety glasses, and a bucket. Candidates are rounder and lighter than solid rock; a soil pipe cutter opens them cleaner than a flat smash.

When is the best time to visit Grubb Lake and Mud Lake?+

The most comfortable months at Grubb Lake and Mud Lake are March to November.

How do I get to Grubb Lake and Mud Lake?+

Open the directions link to navigate to 40.06010, -76.44938 in Google Maps. The nearest road is Ironville Pike.

More rockhounding in Pennsylvania

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Open Grubb Lake and Mud Lake on the map

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