A sequence of sedimentary and volcanic rock totaling more than 33,000 feet in thickness is exposed in the northern part of the Olympic Peninsula, Washington. These rocks range in age from early Eocene (?) to Miocene and occur in a structural belt that was undergoing deformation during most, if not all, of Tertiary time. Lithologic units recognized include the following, listed from oldest to youngest.

Unnamed sequence of argillite and graywacke
Crescent formation: splitic pillow lava, flow breccia, and tuff
Unnamed unit: siltstone
Lyre formation: conglomerate and sandstone
Twin River formation of Arnold and Hannibal, 1913 (to be redefined): sandstone and siltstone
Clallam formation: sandstone and conglomerate

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