Hmmmm ... that looks familiar - is it located on the south slopes of Signal Peak in SW New Mexico by chance? I ran across something similar in that area a while back. In all probability, rocks like these were placed as markers by hikers, hunters, prospectors, etc. It seems quite a stretch to call it "Spanish" IMO.
If this was layed up by human hands, then it was done for a reason! Maybe a grave? A spot one must be to take a compuss reading? You might check out from there for 1 or 200 feet in a circle to see if you can see something else.