I think mushrooms could be a more parsimonious answer than UFOs.
Could tie in with their rituals as well?

That's pretty neat. You should have taken some of the grass as a sample and brought it back... maybe someone could examine why its a different color to the rest.

I don't know, nothing much to say, its pretty neat.

I think that there was a second ring, the picture I have seems to show that, but the wiki doesn't.
Some mushrooms grow in a ring, but this is there all the time according to the man I spoke with. It is also in the wiki picture. I don't know when that one was taken. Mine was taken last November. Do mushrooms grow all year or are they seasonal?
If it's another type of grass, why would it grow in a rather perfect ring? Most grasses tend to run or clump.

I checked on fairy ring fungus. It does produce a deep green circle, but it also produced fruit (mushrooms) and it continues to grow away from the center. These rings are stable and the grass inside and around them is not altered.
If this area was used for sacrifice (and there is no evidence to support that) how much blood would have to be spilled to last since 700AD?

Interesting question.

One thing that came to mind is that it could also mark a geological or man made feature. You can tell places that have been modified by humans because of differences in the soil (and that changes the plants that grow there.) The first thing I'd want to do is some botanical research!

Fungus rings are known (fairy circles) ... they're not hallucinogenic mushrooms, though they may not be mushrooms that are safe to eat. I'm not familiar enough with the botany of Central America and Mexico to say whether or not those things grow down there.

But what an interesting thing to find!