Spearfish Canyon

Spearfish Canyon is a limestone gorge on the northern edge of South Dakota's Black Hills, followed by the Spearfish Canyon Scenic Byway (US-14A) between the towns of Spearfish and Cheyenne Crossing. It sits within Black Hills National Forest, cut through three main rock layers — Deadwood Shale, Englewood Limestone, and Paha Sapa Limestone — with caves and fossils common in the uppermost Paha Sapa unit. Beyond the scenery, Lawrence County is regionally known among rockhounds for geodes: baseball-sized nodules lined with amethyst, quartz, and chalcedony that turn up in stream gravels around the canyon and nearby Whitewood Creek, alongside silicified wood. Wikipedia's own geology coverage of the canyon doesn't mention any of this — the mineral reputation comes from rockhounding-specific sources, not the standard geology writeups.

Follow the Spearfish Canyon Scenic Byway (US-14A) between Spearfish and Cheyenne Crossing, Lawrence County. Pull-offs along the byway provide access to streamside gravel; no single named collecting trailhead was confirmed for this coordinate.

General-area inference: surface and gravel-bar picking in creek beds along the canyon and Whitewood Creek is the standard method for geodes and silicified wood — no digging into canyon walls.

Spearfish Canyon sits within Black Hills National Forest; most of the canyon corridor is public USFS land, though roadside pull-offs along the scenic byway are the practical access points and some adjacent land may be private inholding. Confirm current Black Hills National Forest rock-collecting guidance directly rather than assuming a blanket national quantity limit — individual national forests sometimes set stricter local rules.