Highway 20 Fun

Saying good-bye to the North Cascades was a lot harder than I'd imagined. Spending a month in the wilderness made me really appreciate America's preservation of many forests.  I learned so much (and looked at enough maps) in the few weeks I was there that I was able to name many of the bigger landmarks while looking out the window on our flight out of Washington, like the Columbia River, Route 2, and Lake Chelan.

We spent a good part of our last week in Washington studying the rocks around Highway 20, the northernmost road in the state.  There, we were looking primarily at the golden horn batholith, a pluton that weathers to a pretty golden color.  We came across a few stunning outcrops and clear contacts between the golden horn rock and a volcanic rock.  In the picture below on the left, you can see human-sized xenoliths, or pieces of the country rock, that fell into viscous magma.  The magma solidified before the xenoliths had time to melt, leaving clear and impressive boundaries between the two bodies. Chill margins of smaller crystals that solidified quicker than the rest of the magma are often found bordering the xenoliths. On the right is a much smaller boulder exhibiting the same characteristics that we found on a hike the next day.

Equally as interesting, miarolitic cavities cropped up occasionally as well.  Miarolitic cavities form when pockets of gas exist in a pluton near the surface of the earth (about 1 km or less). In the space, crystals have room to grow without many obstacles. See below a picture of a crystal about 3 cm long in a miarolitic cavity in a boulder at the base of the xenolith-filled wall, pictured first in this post.

Finally, the funniest part of our time on highway 20 was watching Mike and Yuem teetering on a log as they crossed a river where a bridge used to sit.  Pay attention to the notice on the log.

Emily Shorin