From this vantage, you are looking down on the north slope of Tempe Butte.  The foreground shows the bedrock of the Tempe Beds poking through a thin veneer of colluvium or talus.  In a similar bedrock position on the south side, the bedrock is coated with black rock varnish.  However, the bedrock here on the south side lacks the rock varnish.

The colluvium on the Tempe Beds, as seen here, is only a few centimeters thick.  In contrast, the colluvium on the south side tends to be much thicker — several feet thick. 

Why do you think the colluvium is so much thinner here on the north side of Tempe Butte compared with the south side? (If you don't remember what the south side looks like, click here)