Some Tuff Work

After almost two weeks of looking at igneous rocks, which are formed by cooling magma, Mike decided to switch things up and look at a set of sedimentary rocks for a day.  Sedimentary rocks are important because they have the potential to record the environment at the surface of the Earth where they are deposited.  In our case, we were using an old thesis (McClincy, 1986) as a guide to find some volcanic tuffs.  Tuffs are formed from volcanic ash expelled during an eruption.  Dating these rocks could help put time constraints on the deposition of sediments in the area, and will help correlate their history with the history of some of the igneous rocks that we've been studying. 
We drove to an area of the North Cascades where McClincy had described tuffs and found some of the rocks in road cuts along the canyons in which they were mentioned.  This helped us get a sense of the type of rocks we were looking for.  We noted sediment sizes and textures. Then we set off for our real goal - to sample tuffs that were deposited during the right time period.  After bush whacking up a steep hillside for 300-400 feet of elevation and discovering a trail at the top, we spent the rest of the day looking for and sampling layers of flaggy sandstone with rhyolite clasts that fit the descriptions in McClincy's thesis. Hopefully the samples we took will be of similiar age to the igneous rocks we mapped during our first week.

The view from the top of the ridge where we searched for tuffs.

Emily Shorin