Illinois River: Agate & Jasper Rockhounding in Josephine County, Oregon

Quick details

Access

Check locally

County

Josephine County

State

Oregon

Nearest road

Forest Road 4201-027

Coordinates

42.24764, -123.69263

Geology at Illinois River

This spot sits on Western Klamath Terrane; Smith River Subterrane; Josephine Ophiolite, mapped as peridotite and serpentinization: massive that formed roughly 200 to 145 million years ago. Metamorphic rock like this weathers into resistant float, and minerals that survive transport typically concentrate in nearby drainages.

Mapped unit

Western Klamath Terrane; Smith River Subterrane; Josephine Ophiolite

Age

200–145 Ma (Jurassic)

Rock types

peridotite and serpentinization: massive

Elevation

1,200 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 Illinois River

Best months: September to June. Typical highs run 95°F in midsummer and 50°F in midwinter, with winter lows near 33°F. Summer heat here is intense, so carry more water than you think you need and work the early morning.

Climate normals: NOAA 1991-2020 monthlies, CAVE JUNCTION 1 WNW station (7 mi away), adjusted for elevation.

Land & collecting status

Confirm rules before collecting

Land status here is not confirmed. Verify with the managing agency before collecting — federal, state, and tribal rules differ.

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.

State guidance last verified: April 1, 2026

• BLM Oregon/Washington — Rockhounding & mineral material
• Oregon Department of Geology and Mineral Industries (DOGAMI)
• Oregon Parks and Recreation Department — beach collecting rules
• Community submissions reviewed against published agency rules

Found at Illinois River

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

• AgateEncyclopedia →
• JasperEncyclopedia →
• Josephinite