Friends of the Desert Mountains (FODM) offers a hand-on workshop for volunteers to learn how to remove/paint over graffiti on the trails. Over the past few years this program has aggressively attacked graffiti on trials in the Coachella Valley. For my training we went to a local trail in Palm Springs that had a few graffiti covered rocks that had been reported to FODM.
Step 1: Identify the base color in the rock and apply a thin wispy coat to cover the entire area.
Step 2: Throw sand on the still wet paint to try and create a color gradient that matches the rock surface.
Step 3: Recognize you can only accomplish so much with paint. Although it doesn't look impressive up close. When we stepped back on the trail 10-20 feet away it was a lot less noticeable.
Here is another before and after picture.
After completing the workshop, I received my graduation gift/supplies to address any graffiti I find when hiking. Research indicates two positive outcomes from this program. First, when mountain and trail graffiti is covered over people are less likely to add new graffiti to the area. Second, the coverage coat of paint applied to the graffiti is more durable than originally thought. Graffiti has not bled through the cover coat applied by FODM volunteers.