I really need to put eyes on the petroglyph to see enough details to form ideas. I can comment on what I'm seeing in the photo from a novice perspective, but all of this is purely conjecture. It appears the lower half of the panel may be missing or eroded. The carving appears to be with a metal tool since the lines are so narrow and clear. This is odd, unless the artist received a metal tool from somewhere. The most distinctive things looks like there are two fellows with hats or helmets. This means white man, possibly Mexicans, maybe Spanish. They are likely the subject of the panel. The upper right fellow may be trying to reach something (travel) in the direction he faces. It is unusual to see a horse with so much detail. I think this would only be done if the artist was seeing a horse for the first time and wanted to show others what this new creature looked like. The horse appears to be carrying a pack or crate. The direction of travel is indicated by where the horse is facing. Ahead of the horse might possibly be simplified symbols for going between a rising feature on the right and descending feature on the left, like a saddle between two different height hills. It is more likely this symbol somehow represents nearby geography. The horizontal arc with an "x" below is unusual. I have not seen an "x" to show a spot where "something is hidden" below; they would use a pecked dot. The circular shape on the far left with a tail might be "veer to the left to see something held." The two U-shaped symbols together bottom right likely signify geography. Perhaps look over the edge and back to see something. The cracks in the rock may also be part of the message, likely showing some geographic feature. One really needs to be at the petroglyph site to see the symbols and view all of the surrounding terrain and geography before interpretation might occur.