Part of the Sprinkler system?

Found this in the ground, buried in the mulch area of the front yard. Black plastic top with a green cap within an enclosure.

Is this a part of the sprinkler irrigation system? Seems odd because there are no sprinklers out here, just some drip lines in other areas of front yard. I don’t maintain or control anything here, it’s all HOA responsibility and a landscaping contractor to maintain all front yards in the neighborhood.