Kirkwood Mountain Resort.
It’s that time of year when people head up to the Sierra Nevada Mountains for some great skiing and snowboarding. This season is looking to be a good one with a handful of big storms dumping huge amounts of snow on resorts and in back-country terrain. Although deep snow cover obscures the view of some of the geology, the views from chair lifts and other vistas while skiing is a fantastic opportunity to think about the geologic evolution of these mountains.
My favorite ski area in the Sierra is Kirkwood Mountain Resort, which is along State Route 88 approximately three to three and a half hour drive from San Francisco and 20-30 minutes from the town of South Lake Tahoe. In addition to great terrain, Kirkwood has some fantastic geology, some of which you can ski right up to and check out in detail.
The rocks exposed at the surface on the mountains of Kirkwood are various volcanic rocks ranging from about 6 million to 15 million years old (depending on exactly where you are). The volcanic deposits at Kirkwood are nothing like the smooth lava flows you might see on the Big Island of Hawai’i. They are more similar to the recent volcanic deposits seen on the flanks of and in areas adjacent to the Cascades volcanoes in northern California, Oregon, and Washington.
Many of the cliffs exposed at Kirkwood during the winter are beautiful volcanic debris flow deposits that have up to boulder-sized chunks of igneous rock within a fine-grained rock. These rocks are interpreted to be the deposits of mixtures of mud, sand, and volcanic rock debris that flowed down the flanks of the now-extinct volcanoes. I forgot the name of the specific trail — please comment if you know — but there is a great run where you can take a short break to catch your breath and walk up to some outcrops of these debris flow deposits.
So, next time you’re sitting on the chair lift waiting to take that next run, look around at these beautiful mountains and picture the ancient volcanic landscape that created the terrain you’re skiing.