Oceanside & Tunnel Beaches: Agate & Jasper Rockhounding in Tillamook County, Oregon

Quick details

Access

Check locally

County

Tillamook County

State

Oregon

Nearest road

Maxwell Mountain Road

Postcode

97134

Coordinates

45.46230, -123.97243

Geology at Oceanside & Tunnel Beaches

This spot sits on Columbia River Basalt Group; Grande Ronde Basalt, mapped as basalt conglomerate, hyaloclastic breccia, cementation: clays, zeolites, clacite; lithology: palagonitic, carbonaceous mudstone, mineralogy: micaceous, carbonaceous sandstone, pillow breccia, basalt flows, dark to light gray; lithology: tholeiitic, pillow flows, and dark to light gray; lithology: tholeiitic basalt that formed roughly 23 to 5 million years ago. Fossils are uncommon in volcanic rock itself; look to any interbedded sediments and ash beds, where plant material and bone are typically preserved.

Mapped unit

Columbia River Basalt Group; Grande Ronde Basalt

Age

23–5 Ma (Miocene)

Rock types

basalt conglomerate, hyaloclastic breccia, cementation: clays, zeolites, clacite; lithology: palagonitic, carbonaceous mudstone, mineralogy: micaceous, carbonaceous sandstone, pillow breccia, basalt flows, dark to light gray; lithology: tholeiitic, pillow flows, and dark to light gray; lithology: tholeiitic basalt

Elevation

50 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 Oceanside & Tunnel Beaches

Conditions here are workable year-round, with typical highs from 52°F in winter to 68°F in summer.

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

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 Oceanside & Tunnel Beaches

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

• AgateEncyclopedia →
• JasperEncyclopedia →
• CalciteEncyclopedia →
• FossilsEncyclopedia →
• Zeolite