One thing I've read is that the concentric circles are a calendar. Each time the family or tribe migrated to that area they add a ring to the carving. The ancient indians in this region where nomadic, they'd typically have lands they'd populate in the summer and in the winter. So the circles might be four different seasons or years that occurred when those people passed through that area. I've read that large spiral rings which I've found out in the desert are supposed to be an indication of water but that doesn't appear to be what that is.
As far as the other symbols your guess is as best as mine. I don't think everything that was carved in stone was necessarily profound or had some deep meaning about their gods or something. Sometimes it may have just been doodle while they were bored watching their mother grind mesquite beans. Granted its no small feat carving into rock and it must have taken a lot of work but without a written language it may have just been ancient man saying "I'm here".