On that map of the ash fall, how deep was the ash at the outer perimeter, for example, northern Texas?
Based on this link: https://gsa.confex.com/gsa/2001AM/finalprogram/abstract_27084.htm
There are Lava Creek (Yellowstone) ash deposits as much as 1.5 meters thick near Amarillo, and there’s no indication as to whether those exposures are unmodified by compression or other geological processes, so it could have been more originally. Closer to the caldera, in Wyoming, the Lava Creek deposit is nearly 600 feet thick.