Yes it was a gravel pit many years ago.
In the 70s there was a small publication, delivered by your postman, called Everywhere West.
Some of the first reports about the LA&SL were published in it. By reports I mean folks drove in and along the RoW eventually all the way from Afton , through the washes , around the Crestline Horseshoe to Utah, noting sidings and other prominent RR features, plus power and cars of any trains encountered, with tiome aand place.
Previously most information had been by Walter Thrall and a few photos by Steinheimer. Basin at that time had just been used as a dump for old UP records- tossed from RR cars and given a thin to moderate cover of gravel. Off-roaders found the easy stuff that was near the surface- who knows what may still be deeper.
I retrieved a few sheets of old valuation worksheets just to say I did- counts of rail sizes on the OSL IIRC-- So I concluded anything exciting was probably a needle in a haystack buried in a former gravel pit.
Your backhoe- don't leave home without it