Spiden Island and the Rain Shadow

I got a good look at Spiden Island in the northern part of the San Juan Islands. It has a decidedly non evergreen state look about it.

Spiden Island from the southwest

The island has such a dry look about because it is in fact dry. Spiden is located within the rain shadow of the Olympic Mountains.

View from the same location looking southwest to the Olympic Range

Spiden Island (USGS)

Solar aspect makes a difference as well. The southwest slopes of the island are mostly grass and the steep northeast shading portion of the island is tree covered. For a time an owner of the island had zebras on the island as well as some other exotic animals. The linear slash into the trees on the northwest end of the island is a grass covered landing strip. I have been to Spiden twice for work and it is a dry place. One visit coincided with a small forest fire caused by lightning hitting a tall Douglas fir along the summit ridge. Spiden Island is underlain by the Nanimo Formation - more on that on some future post.

Location of Spiden (USGS)

Spiden's dryness as well as other areas in the San Juans is primarily caused by the Olympics which create a rain shadow from storms approaching from the southwest. The mountains on Vancouver Island create some rain shadow effects as well with the east coast of Vancouver Island where the vast majority of islanders live referred to as the Sunshine Coast.