Tunnel Brook: Gold Prospecting in Grafton County, New Hampshire

Plan your visit

Generally open to casual rockhounding

County

Grafton County

State

New Hampshire

Nearest road

Tunnel Brook Road

Coordinates

44.09300, -71.90000

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.

Access note: White Mountain National Forest, Benton, up Tunnel Brook Road off Route 112. A free national forest gold-panning permit is required, and equipment is limited to a gold pan and small hand tools, with sluices, dredges and motorized gear prohibited. Tunnel Brook Road is unpaved and can be impassable when wet.

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 Tunnel Brook

Comfortable months (45 to 90°F highs)

Best months: April to October. Typical highs run 76°F in midsummer and 25°F in midwinter, with winter lows near 6°F.

Climate normals: NOAA 1991-2020 monthlies, BENTON 5 SW station (5 mi away), adjusted for elevation.

Geology at Tunnel Brook

This spot sits on Ammonoosuc Volcanics, Bimodal volcanic rocks, mapped as felsic volcanic and mafic volcanic that formed roughly 470 to 445 million years ago. Gold in volcanic terrain like this is usually tied to old vein systems and the gravels that drain them, so nearby washes tend to carry the color.

Mapped unit

Ammonoosuc Volcanics, Bimodal volcanic rocks

Age

470–445 Ma (Middle Ordovician to Late Ordovician)

Rock types

felsic volcanic and mafic volcanic

Elevation

1,680 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.

• White Mountain National Forest
• New Hampshire Geological Survey
• New Hampshire State Parks rules
• Community submissions reviewed against published agency rules