Castle Rock

The outcrops are the Idaho batholith breaking the surface. Its granite and granodiorite formed as magma cooled as much as ten miles underground in the late Cretaceous, roughly 64 to 100 million years ago, when Idaho was the western edge of the continent; uplift and erosion later laid it bare. Rounded forms like these come from spheroidal weathering, as water works into the rock from every side and decayed grains flake away in shells. The Geological Survey maps granodiorite of the batholith at nearby Cat Creek Summit.

What the plaque says

Castle Rock Up toward Camas Prairie, a road goes by Castle Rock and other eroded granite outcrops that were landmarks on Goodale's Cutoff, an Oregon Trail route that came this way. Emigrants generally had not seen large granite rock formations of this kind, and Idaho offered a number of good opportunities, both for Oregon and California travelers. Castle Rock and its neighbors were outstanding examples along Goodale's Cutoff, used primarily from 1862 until automobiles replaced wagon traffic more than 40 years later. 353 Text prepared by the Idaho Historical Society Marker made & installed by Idaho Transportation Department

Where it stands

More markers nearby

• Goodale's Cutoff — steps away
• Gold Mines — 1.9 mi
• Toll Gate — 14 mi
• Rattlesnake Station — 20 mi