Castle Crags: Rock Older Than the Cascades

Look to the east. Those rock towers rising above the canyon are roughly one hundred seventy million years old.

To put that in context: the Cascade Range, which includes Mount Shasta and Mount Rainier and every other volcano you can see from here, is geologically young, between one and five million years old for most of its major peaks. Castle Crags are older than both, a remnant of what geologists call an exotic terrane, a section of ancient Pacific Ocean seafloor that was scraped off its plate and accreted onto the North American continent through the slow violence of tectonic collision.

What you are looking at are granite plutons, intrusive rock that formed when magma cooled underground and was later exposed by hundreds of millions of years of erosion. The towers reach elevations of approximately six thousand five hundred feet. Interstate Five runs below them, following the Sacramento River Canyon corridor that Southern Pacific built its railroad through in the eighteen sixties and seventies.

The granite does not care about the interstate. It was here for several hundred million years before the first road was built in this canyon, and the geological forces that move plates and mountains operate on timescales that make a highway seem like a feature of a Tuesday afternoon.

The climbers who go up those towers are moving across rock that has been here since before there were fish with backbones. It holds them fine.