If you look closely you'll see a milky, opalescent, bloblet at the end of the abdomen, between the inner-hind edges of the wings. I'm guessing that's an egg and this Tebenna gemmalis was a female ovipositing. Unfortunately, I didn't notice this at the time, but only in scrutinizing the photo long afterwards...so I didn't take the opportunity to examine the presumed egg or host plant carefully in the field.

I believe the plant here is Mules Ears (Wyethia mollis), but there's a possibility it may have been Arrow-leaved Balsamroot (Balsamorhiza sagittata). The two plants are similar looking and easy to confuse. Both are perennial composites (Asteraceae) which occur in the region and are mentioned as host plants for T. gemmalis: B. sagittata in Powell & Opler(1); and W. mollis in this Essig Museum record. The simplest character distinguishing the two plant species is leaf shape: tapered at base for W. mollis; sagittate at base (i.e. lobed...like an arrow-head) for B. sagittata. I didn't get any shots of the leaf base, but the tomentosity and my general impression at the time make me lean towards W. mollis, which is also a more common plant in that area and habitat.