Hiking in Sedona - Day 3 - Chimney Rock & Thunder Mountain

Day 3 saw tired legs (at least for P) so a shorter, 5 mile hike, round Chimney Rock & across the front of Thunder Mountain.

P looking tired, Chimney Rock in the background;

Views from the hike;

Thunder Mountain;

Jakki at the top having scrambled up a peak;

So what we'd like to know is, why are there the different layers in the rock? And what causes them to be different colours and why are the white layers harder than the red layers?