Explanation of ripple marks, courtesy of The Amazing Fred Spicker, aka "SP's Favorite Geologist":

"Think in terms of a really shallow area with ripple marks formed on the bottom - you have probably seen these at the beach near shore. Then, a change of some sort takes place and fine sediment is laid down on top of the ripple marks. Then, the whole works gets deeply buried and turns to rock. When the rock becomes exposed and weathered, the rock formed from the fine sediment that covered the ripple marks is weathered away more quickly, leaving the nicely preserved ripple marks behind. Not really large enough to be called wave marks."

Thanks, Fred!

Ripple marks etched in the rock, near the summit of Swiftcurrent Mountain. Adjacent to the trail. 24 August 2007.