Googled, couldn't really find anything, so thought I'd ask here. Found a yellow plastic pipe in the middle of the backyard, goes down about a foot or so, white valve or switch type of thing at the bottom (debris was partially covering it up, didn't have anything long enough to get the stuff out). Almost literally in the middle of the backyard, not in line/in between our gas meter and our neighbor's, no sprinkler system, and not part of some other lot that got absorbed into this one (houses were built in the Venice neighborhood in the 1950s, so these lots have always been the same). Pic attached, wondering if anybody has any idea what it might be?

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