No wonder we never see them! They're tiny. We always expected them to be big like people, but these are Tiny Aliens, and their tiny spaceship looks like an ordinary decon container.
Update 4/27/21: The cache has been moved closer to the trail in a, hopefully, PO-free (or mostly so) area. Hint and coords updated. Not hidden as originally designed by oldbadger, but a full restoration is not feasible. Hopefully the new spot will not be at too great a risk of muggle discovery, but it will definitely be a more "friendly" location for cachers. WERDAVE for oldbadger.