I know this is crappy documentation, but despite my best efforts I couldn’t get a good photo of these fish, so I illustrated what I could see, based on the photos I did manage and impressions in the field.

22 July 2018

Small group observed darting in and out of the shade of a boulder in a rather shallow pool in a small stream. Three-spined Stickleback also present.

Derrydale Creek, along Hwy 33 in Ventura County, Southern California.

Major field marks I noticed:

Dark marking, blurry crescent shaped, black with obscure red tones (edging?) – I'm now starting to wonder if maybe they just had their opercula flared out (making the gills visible and thus the dark black/red crescent).

I think this seems more likely given that the water in this pool was still and very warm, and perhaps thus depleted in dissolved oxygen.