Those are cow bones. They are part of the vertebrae - they look like they're a couple of years old. I usually come across the whole cow, minus the head.
When coyotes take down a big animal, they circle it and tease it until it finally gets worn down and falls. For some reason that I don't understand, they take the head and drag it off. It looks like you were in a wash that had been flooded recently from all the vegetation and debris.
I do the same thing going out into the desert. It's eerie, quiet, and really kind of neat. I like going into areas when the only man made thing in view is my Jeep. I have been out though when I know I was being watched by border crossers. I have also been close enough to smell the sweat - I know they left the trail or wash and were somewhere hiding until I left. Now THAT is an unsettling feeling.
