the northern end, near the Olympic Peninsula. The interesting thing is: backing out this rotation restores the Coast Range to an earlier position nearly juxtaposed against the OWL. argues that the Coast Range (believed to be seamounts that had previously accreted to the continent) were rifted away from the continent starting about 50 Ma ago (mid-Eocene). This interpretation implies a "back arc" of magmatism, probably fed by a subduction zone, and possibly implicated with the intrusion of various plutons in the North Cascades around 50 Ma. Curiously, this is just when the Kula–Farallon spreading ridge passed under the OWL (discussed below). found a spurt of rapid rotation around 45 Ma ago. This may be when this block was impinged by the Sierra Nevada block of California; note that around 40 Ma ago there was a change in the direction of the Pacific Plate (possibly due to collision with another plate). (The cause and nature of the rifting does not seem to have been worked out yet. Certain complications in the subduction of the Kula and Farallon plates may have been involved.) During this rotation of the Coast Range the block of continental crust that is now the Blue Mountains (on the eastern side of the KBML) was also rifted away from the Idaho batholith, and also rotated about 50 degrees, but about a point near the Wallula Gap (or perhaps further east). In the resulting gap the crust was stretched and thinned; the buoyancy of the hotter mantle have contributed to the subsequent rise of the Wallowa and Seven Devils Mountains, and perhaps also with the irruption of the Columbia River basalts and other basalt flows. While the rigid-block rotation model has much appeal, many geologists prefer another interpretation that minimizes whole–block rotation, and instead of rifting invokes "dextral shear" (resulting from the relative motion of the Pacific plate past the North American plate, or possibly from the extension of the Basin and Range province) as the primary driving force. The large values of paleomagnetic rotation are explained by a "ball bearing" model: the entire Oregon block (western Oregon including the Cascades and southwestern Washington) are deemed to be composed of many smaller blocks (on the scale of tens of kilometers), each of which rotates independently on its own axis. Evidence of such small blocks (at least in southwestern Washington) has been claimed. Later work has attempted to work out