Many of the rock shelters in Joshua Tree National Park are at least partly formed by a natural erosion process called exfoliation. There are different theories as to how exactly this process works. The theory currents in favor is that it is caused by rain breaching the surface of the granite and interacting with the minerals in the rock, causing expansion which over time causes the surface to flake off.

This little overhang clearly shows an area that exfoliated recently – “recently” used here in the context of the age of the boulder! Look for the light colored patches in the brownish area in the center of the photograph.

Look down and to the right of the exfoliated area. There is some pigment there!

Regardless of exactly how exfoliation happens, it is a fact of life for granite boulders.

The hollows that form in this way often make attractive shelters and many indeed show evidence of past habitation.

Sometimes these shelters have pictographs painted in them. I found the remnants of such a site while wandering around Joshua Tree National Park.

A closer look at the remaining pigment, visible almost in the center of the picture.

The design is almost completely destroyed because most of the boulder’s inner surface has flaked off since it was painted but a tiny strip of pigment still remains.

The pictographs may have been rather intricate at one time. All that remains now iare some delicate lines radiating out from the damaged area.

I wonder how many sites we’ve lost in this manner over the years.

There is nothing much to do about a natural process but it serves as a reminder that everything that we know and consider impervious to the ages will eventually wear away and be replaced by something new.

If you happen to find this little site, don’t damage what little remains of it. Eventually it too will succumb to the passage of time.