Neptune Mine near Grays Spring: Fluorite Rockhounding in Pima County, Arizona

Plan your visit

Generally open to casual rockhounding

County

Pima County

State

Arizona

Nearest road

South Sierrita Mountain Road

Coordinates

31.90639, -111.20806

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: Old fluorspar mine area in the Sierrita Mountains. Collect only on open public ground, avoid claims, and stay out of shafts, adits, and pits.

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 Neptune Mine near Grays Spring

Comfortable months (45 to 90°F highs)

Best months: August to May. Typical highs run 91°F in midsummer and 58°F in midwinter, with winter lows near 26°F.

Climate normals: NOAA 1991-2020 monthlies, ANVIL RCH station (11 mi away), adjusted for elevation.

Geology at Neptune Mine near Grays Spring

This spot sits on granitic rocks, mapped as diorite, alkali granite, and granodiorite that formed roughly 185 to 145 million years ago. Plutonic rock like this weathers slowly into grus and boulders, and the most productive collecting is typically in weathered zones and drainages.

Mapped unit

granitic rocks

Age

185–145 Ma (Early Jurassic to Late Jurassic)

Rock types

diorite, alkali granite, and granodiorite

Elevation

4,890 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.

State guidance last verified: April 1, 2026

• BLM Arizona, Recreational Mineral Collecting
• Arizona Geological Survey
• Arizona State Land Department recreation permits
• Community submissions reviewed against published agency rules