It is hypothesized that portions of the northern section of the range were islands during parts of the Eocene era.

[4] The range is part of a broad, plunging structural arch of sedimentary and Tertiary volcanic strata that is being uplifted.

[7] Other plants that grow in the region are huckleberry, salmonberry, thimbleberry, salal, vine maple, sword and bracken ferns and Oregon grape to name a few.

[7][8] Arthropods and molluscs found include collembolans, spiders, beetles, slugs, millipedes, weevils, and various centipedes.

[8] Birds include chickadees, red-breasted nuthatches, kinglets, Western pileated woodpeckers, Oregon Canada jays, California creepers, and Sitka red crossbills among others.

[2] The climate of the range is moderate because of marine influences, and annual precipitation is heavy, varying from 60 to 180 inches (1,500 to 4,600 mm).