Leech River Fault

The Leech River Fault extends across the southern tip of Vancouver Island in British Columbia, Canada, creating the distinctively straight, narrow, and steep-sided valley, occupied by Loss Creek and two reservoirs, that runs from Sombrio Point (southeast of Port Renfrew and Sombrio Beach) due east to the Leech River, and then turns southeast to run past Victoria.

About ten kilometres north the nearly parallel San Juan Fault marks the southern limit of rock of the Wrangellia terrane, which underlies most of Vancouver Island.

[12] More recent interpretations of marine seismic reflection studies align the Goldstream arm of the LRF with the Southern Whidbey Island Fault (SWIF), with splays branching towards Discovery Bay.

They formed between 100 and 84 Ma (millions of years ago) during the Late Cretaceous when the Pacific Rim terrane was crushed between Wrangellia and the North American continental plate, dismembered, and the pieces smeared along what was then the edge of the continent.

It ran it into the edge of the continent and embayed the overlying crust, bending the section of the Wrangellia—Pacific Rim contact now known as the San Juan fault to its current easterly orientation.

[20] About 42 million years ago this northeastward force rotated to a northerly direction which, striking the SWIF more obliquely, caused the strike-slip movement that offset the LRF past Victoria.

The Leech River Fault across the southern tip of Vancouver Island and the Tofino, West Coast, Hurricane Ridge (portion), San Juan, Survey Mountain, Devils Mountain, and Southern Whidbey Island Fault , and the projected extension of the Leech River Fault through Discovery Bay ; all dip to the northeast. Stippled area is top of the Pacific Rim Terrane . Also shown: Cape Flattery , San Juan Island , and the cities of Port Renfrew , Sooke , Port Angeles , Port Townsend , and Victoria . The northeast extension of the San Juan fault may be an older feature. [ 1 ] Newer studies show the Leech River fault more closely aligned with the SWIF. [ 2 ]
The Olympic–Wallowa Lineament (OWL) marks the approximate continental margin in the Late Cretaceous . The northeastward impact of part of Siletzia formed an embayment as indicated by the Darrington-Devils Mountain fault and the mélanges originally in front of the continental margin.