Closeup of a Solenopsis molesta (Thief Ant) on a dead beetle. [p 22]

The beetle is possibly a California Broad-necked Darkling Beetle (Coelocnemis californica) -- or its other local cousin Darkling Beetle (Eleodes dentipes), aka the Dentate Stink Beetle.

Merav & other experts say this is Solenopsis molesta over Pheidole californica.