So I road back, and found it again, and it'd already been nicked once, as it'd had flipped over. I picked it up and tried and saw that it was a boost mobile phone, and that the LCD was still working (though the phone was scratched up). Since I didn't want to deal with people I turned it off.
Later I figured out that sprint was the current owner of boost mobile, so I trecked over to a nearby sprint store, and said "I found this, try not to let it end up in a landfill", and then walked out.
(Though what I was actually more concerned about it getting washed out into the ocean.)