You may want to try it a little different Jules . Boulder tracks are hard to spot above 1/mp . However the boulders themselves are pretty bright and gnarly at 4 to 8 mp . If you take the example pic on act and zoom out to your maximum ( eye comfort level ) That you can make out the boulder , you can see the difference in boulders vs crumbly boulders . I've also noticed sussing out downhill from even bigger cliffs can produce pleasing results .
So I would add ,
1. Search ( at max comfortable zoom level ) for boulder producing areas .
2. Zoom in a bit and look for Fuzzy boulders ( being crumbly they wont be as sharp as a whole rock )
3. Zoom in and look for tracks .
Impact areas can be fun too , if they strike an area where they can dislodge material instead of ejecting it .
Looking in the hills finds some prospects also .
All that being said , I have yet to find a good example myself as all of them seem to have just fallen apart and not exploded .
Even went to the poles to see if something fell out of the frost zone/perpetual shadows , and popped .
This is not an easy task no matter how you go about it , but I think you'll wind up with some intensive boulder expertise by the time it's done !