This is way out halfway to the middle of nowhere. Found it years ago while hiking for butterfly photography. I believe the water is an output from some type of suburban water treatment actitivy (an explanatory sign at the back faces an intercity bike trail). The way you can tell they are not natural boulders is to look from the back...
... and see that one of the "boulders" has a door. All of this behind a chain-link fence presumably to keep out meddlers and terrorists.
Next to the door are some real-life boulders. The fake ones are probably some type of cast concrete similar to what modern zoos use to replicate wild environments.
What impresses me is that this community went to all the trouble (and expense) of creating a visually attractive front for this ultimately prosaic process, at a location that is not readily seen by the public (it's not even on a regular hiking trail - I had to walk down a dirt access road from the park). It is mowed on a regular basis and maintained for the benefit of whatever critters happen to fly, crawl, or swim in. Kudos to someone.
It's located here, for any locals who want to visit.