Todd, blocks of crust can rotate (spin) if caught up in a shear zone, The western Transverse Ranges, which are the East-Wast oriented faults, Islands, Mountain Ranges north and west of Los Angeles, have rotated 90 deg clockwise in the last 18 million years or so. Magnetite in rocks records the past magnetic field as well as the present one. The best magnetization is usually in volcanic rocks, especially basalt. But, there can be remnant (old) magnetization in certain sedimentary rocks also. Oriented cores are collected and the magnetic field in the cores measured as the core is heated (for example). The heating removes the present-day magnetization. The lab is shielded from the magnetic field. If the paleo-magnetic pole is oriented to the east or west and not to the north or south, the rock the core was taken from must have rotated. There are reference poles for different times in the past.

HW is headed to Paris to work in a paleo-mag lab for a week in January: probably on sea floor samples to see small variations in intensity of the field over the last few thousand years, to date lava flows. Guess I should ask her.

So, I was just saying the these types of measurements have been done in parts of the Mojave desert.
Chris