Hi there,
My experience of Catharus thrushes is limited to vagrants here in Ireland: two different Grey-cheekeds and one Hermit. Also, I am aware that many 'familiar' species occur in different races on the west coast, some of which can be quite different to those which straggle to western Europe (and would thus potentially throw me off the scent).
Nevertheless, based on what can be seen in this less than clear pic, I am left wondering whether or not Grey-cheeked is a possibility in Yosemite in October? The cold-looking upperparts, relatively plain-looking face etc seem to match that species, though it is hard to be sure based solely on one image.
Regards,
Harry