Pennington Mountain: Calcite & Celadonite Rockhounding in Mercer County, New Jersey

Plan your visit

Generally open to casual rockhounding

County

Mercer County

State

New Jersey

Nearest road

Woodsville Road

Postcode

08525

Coordinates

40.36165, -74.80631

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

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.

Best time to visit Pennington Mountain

Comfortable months (45 to 90°F highs)

Best months: March to November. Typical highs run 86°F in midsummer and 40°F in midwinter, with winter lows near 22°F.

Climate normals: NOAA 1991-2020 monthlies, EWING 3 WNW station (6 mi away).

Geology at Pennington Mountain

This spot sits on Passaic Formation, mapped as siltstone that formed roughly 235 to 175 million years ago. Sedimentary rock like this erodes unevenly, so the most productive collecting is typically along fresh cuts, badland slopes, and active drainages.

Mapped unit

Passaic Formation

Age

235–175 Ma (Late Triassic to Early Jurassic)

Rock types

siltstone

Elevation

270 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.

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.

• New Jersey Geological and Water Survey
• Monmouth County Park System, fossil collecting rules
• Sterling Hill Mining Museum
• Community submissions reviewed against published agency rules