What do you mean by "sand flies"?
It looks like they are brine flies (Ephydridae; prob. Ephydra riparia. Sand flies usually refers to Psychodidae: Phlebotominae which a small gnat-like blood feeders. They are vectors of some pretty nasty diseases.
Holytape; Thanks for the identification. I had no idea what they were called and had even less of a clue as to how to start to narrow down the list. These flies swarmed all over the edge of the Great Salt Lake, moving away in great ripples as I walked along the shore. They did not bite or otherwise show any interest in me other than moving away.
I'd read in a history about the Great Salt Lake that large numbers of which insects which I'd always thought were probably mormon crickets that had been driven over the lake and died would accumulate in vast windrows on the shores and were considered a something of a salty snack by the locals. When European settlers first introduced commercial ocean shrimp to the natives they called them "sea crickets" since to them that is what they tasted like. I've always wanted to go back to give 'em a taste myself. I don't suppose you gave them a try. Next time, maybe.