here). (Although southeastern Washington is pretty thoroughly covered by the Columbia River Basalts, a borehole in this loop recovered rock characteristic of the craton.) It seems that the OSZ may have been offset, perhaps by the Hite Fault, but, contrary to the regional trend, headed south. If this is a cross-cutting offset it would have to be younger than the OFZ (less than 70 Ma), and older than the OWL, which it does not offset. That the OWL and the OFZ are parallel (along with many other structures) suggests something in common, perhaps a connection at a deeper level. But this offsetting relationship indicates that they were created separately. Megashears The OFZ (also called the Trans-Idaho Discontinuity) is a local segment of a larger structure that has only recently been recognized, the Great Divide Megashear. East of the WISZ this turns to the southeast (much as the OWL may be doing past the Wallula Gap) to follow the Clearwater fault zone down the continental divide near the Idaho—Montana border to the northwestern corner of Wyoming. From there it seems to connect with the Snake River—Wichita fault zone, which passes through Colorado, and Oklahoma, and possibly further. There is a significant age discrepancy here. Whereas the OFZ is a mere 90 to 70 Ma old, this megashear is ancient, having been dated to the Mesoproterozoic – about a billion years ago. The Snake River—Wichita fault zone is of a similar age. What appears to be happening is exploitation of ancient weaknesses in the crust. This could explain the Newberry "hotspot track": parallel weaknesses in the crust open as the Brothers, Eugene—Denio, and Mendocino Fault Zones in response to development of the Basin and Range Province; magma from the event that initiated the Yellowstone hotspot (and possibly the Columbia River and other basalt flows) simply exploits the faults of the Brothers Fault Zone. The other faults do not develop as "hotspot tracks" simply because there is no magma source nearby. Similarly, it may be that the OWL reflects a similar zone of weakness, but does not develop as a major fault zone because it is too far from the stresses of the Basin and Range Province. This could also explain why the OWL seems possibly aligned with the Kodiak-Bowie Seamount chain in the Gulf of Alaska, especially as the apparent motion is the wrong direction for the OWL to be a mark