NWCS, green) north of the DMF correlates to the Suak and Roslyn Formations just north of Manastash Ridge. All this is explained by right-lateral strike-slip motion on the Straight Creek Fault, which initiated about 50 to 48 Ma (millions of years ago). This is just after the terrane carrying the Olympic Mountains came into contact with the North American continent. These mélanges may have been off-shore islands or seamounts that were caught between the Olympic terrane and the North American continent, and were pushed up (obducted) onto the latter. Other similar rock has been found at the Rimrock Lake Inlier (bottom of diagram), in the San Juan Islands, and in the Pacific Coast Complex along the West Coast Fault on the west side of Vancouver Island. It appears the entire DDMFZ and Leech River fault system was pushed onto the early continental margin from an original alignment along the OWL. This is an important observation because the Strawberry Point, Utsalady Point, Southern Whidbey Island, and various other unnamed faults lying between the DDMFZ and the OWL – all of which converge at the western end of the DDMFZ – seem to be intermediate versions of the DDMFZ. Movement on the southern segment of the DDMFZ that converges with the SCF – the Darrington Fault – was, as on the SCF itself, right-lateral. And like the SCF, strike-slip motion died out between 44 and 41 MA (due to plutonic intrusions). But the western segment – the Devils Mountain Fault – has left-lateral movement. This is because the Olympic terrane is moving (relative to North America) northeast; its continued clockwise rotation is akin to a giant wheel rolling up the western side of the North Cascade crystalline core. The geology also suggests that the DMF is moving obliquely up a ramp that rises to the east, possibly an ancient coastal shore. The Devils Mountain Fault is seismically active, and there is evidence of Holocene offsets. If the entire 125 km length ruptured in a single event the resulting earthquake could be as large as magnitude 7.5. However, there are indications that the fault is segmented, which might limit rupturing and earthquake magnitude. USGS QFFDB Fault #574, Devils Mountain Fault Strawberry Point and Utsalady Point faults Strands of the east-striking Devils Mountain Fault cross the northern tip of Whidbey Island at Dugualla Bay and north side of Ault Field (Whidbey Island Naval Air