I believe it is an underwing moth
Acc'd to our database: 'pollinated by swallowtails...' . This a tantalizing thought! But I've not seen swallowtails on this trail, unless you count Parnassians.
Along the high trail, these were flying upslope; passing through swarms of nectaring Sierran Percopids...
Looks to me like the typical Hemileuca hera? I thought that one was more in Oregon. Since it's so pretty, I'll just post it to bug guide and get their input.
Present in the thousands right after the sun emerged at 10 o'clock.
The local guide calls this the 'forget-me-not moth'.
The wings were particularly nice