Brothers Fault Zone

At the BFZ's eastern end, near the Steens Mountain fault, the zone of surface faulting turns slightly to the south-southeast (possibly due to rotation of Nevada), then follows the Northern Nevada Rift to form the Oregon–Nevada lineament, with a total length of over 75 km (47 mi).

[5] At its west end, just past the Newberry Volcano, the BFZ terminates at the north-striking Sisters Fault, part of the High Cascades geological province.

Aside from aligning with the northwestern edge of several terranes that have accreted to the North American continent (such as the Klamath Mountains on the southern coast of Oregon, and Blue Mountains Province just north of the BFZ), the KBML has no apparent surface manifestation; it is believed to reflect a deeper structure, possible a pre-Tertiary continental margin.

The Brothers Fault Zone is also the locus of the High Lava Plains (HLP) volcanism of central and southeastern Oregon.

One suggestion is that the large blob of molten rock at the head of the plume was sheared off by the advancing edge of the craton, and remained entrained in front of the craton to melt the lithosphere in a broad region, while the tail of the plume was overrun to make the Yellowstone Hotspot track.

Progression of ages of rhyolitic (silicic) lavas and calderas from McDermitt Caldera to Newberry and Yellowstone calderas (red circles: MC, NC, & YC). Numbers are ages in millions of years. KBML – Klamath–Blue Mountains Lineament, HLP – High Lava Plains, EDZ – Eugene—Denio Zone, BFZ – Brothers Fault Zone, SMF – Steens Mountain Fault, VF – Vale Fault, NNR – North Nevada Rift. White arrow shows direction of North American plate, edge of the craton is approximately along the Oregon—Idaho Border, triangles are Cascades volcanoes.