Colorado River Glyphs

I became aware of a bunch of sandstone carvings along the banks of the Colorado River south of Palo Verde, California. Actually, they're not too close to the river but you can tell the river flowed at that location in antiquity. You can see where I learned about the glyphs here at this website. There's plenty of interesting pictures and information about local archeaology.

http://home.earthlink.net/~blhtvl/index.html

So while visiting California, I decided to make the trip and see the glyphs for myself. These are much different than the Hohokam glyphs I usually see in the area where I live. They're carved in sandstone, so they're not as resistant to the elements when compared to glyphs carved into harder stones. There are plenty of examples of historic graffiti, some dating back to 1915. It's mostly abstract stuff, but I did find one that looked like the head and forearms of a frog.
This area was populated by the Yuman speaking tribes, specifically the Mojave and Quechan. But the glyphs here didn't look like the ones seen at Pilot's Knob or Newberry Peak, both being areas of religious significance for the Quechan.
The significance of these glyphs is anyone's guess. It could represent the flow of the river, and I'm at a loss to describe the columns and rows of indentations. That's ok though, I enjoy looking at these things much more than I do trying to figure them out.