Geology in the West Coast State Quarters

During a recent conversation with Bob Lillie of Oregon State, author of Parks and Plates, he pulled three quarters out of his pocket and showed me a neat little geology lesson contained in the Washington, Oregon, and California coins.

The Washington quarter depicts Mt. Rainier, a young and potentially active volcano of the Cascade Range.

Crater Lake, featured on the Oregon quarter, is what's left of a Rainier type volcano that erupted violently some 7000 years ago, and then, perhaps on the same day, collapsed back in on itself leaving the caldera that is familiar to so many of us today. As a neat aside, Bob pointed out that the thickness of the quarter pretty much represents the depth of the lake at the same scale as the engraved image on the coin.

The granite batholith of Yosemite is chilled magma, now exposed at the surface of the earth, that never made it to the surface of the earth to erupt. It is what we would likely find if the younger Cascade volcanos eroded away to expose the intrusive rocks below them. Interestingly, the relative dates of statehood match the relative ages of the geology depicted on the coins.
Thanks Bob!

Created on ... October 17, 2008