He should have been flying above 12,000', assuming Tioga Pass is the highest point on the route.
Discussion
here.
"
FAA Advisory Circular AC91-36 defines the surface of a National Park area as: the highest terrain within 2,000 feet laterally of the route of flight, or the upper-most rim of a canyon or valley. Simply stated, find the highest ground on your flight path and add 2,000 feet to your cruising altitude."
