Lytta funerea is a pretty black species with a small orange spot on the top of the head (vaguely discernible in one of the pictures). Caution is required, however, in identifying black blister beetles in the Western US. There are several species that are black and have a small orange spot on the head. Lytta funerea is different from these in having nearly straight mandibles. It is also the only one of these species lacking clear pads on the tarsi (the segments making up the "feet").
The habitat around Lost Lake in September is dry. Dragonflies and wasps are out and about but not many other things are. Lytta beetles are known to parasitize bees of the family Anthophoridae. A young beetle larva, once it has emerged from the egg, is very active and finds its way to a flower. When a bee arrives to feed, the small larva (called a triungulin) quickly crawls aboard and is carried back to the bee's nest where it begins to feed on the developing brood. As the larval beetle grows it turns into a sluggish grub and will eventually isolate itself to pupate. These beetles were all glossy black and seemed to have recently emerged.
Here's a habitat shot with tarweed and oaks near where the beetles were seen.