Was that really at 9500'? What elevation does the tree line stop at?
the tree line gradually gets lower the closer to the poles you go, eventually it stops at sea level. I think Mt Mckinley in Alaska its 2500'ish and here in Vernal its around 11400'. It also depends on if you are on the north or the south slope.
Vernal Utah, witch is near Utah highest peak, is 40degrees north. So where they were at the tree line couldn't have been less than 10000'.