I have grown this species, C. scabrida for several years. i have found that it is not picky about the assumed hosts it associates with but have found that the seed never germinates without one. In the case of the photos Aquilegia jonesii and Penstemon idahoensis are the presumed hosts.
Is it tolerant of summer drought?
This plant seems pretty resistant to drought. We only get around 10 or 11 inches per season(if we are lucky), i have not noted the wilt that some of the other Castilleja species often get in the heat and drought of the summer. Like i said, it seems to need a host to germinate it likes Penstemons, Phlox, Aquilegia and Leptodactylon as far as i can tell. Here is a photo that somehow did not appear on the first try.