It's unlikely to be G. firmus as neither subspecies is known to occur west of Texas. Unfortunately, it's often very difficult to distinguish between Gryllus spp. without analysing their songs. It's possible that this could be either G. integer Scudder, 1901 or G. rubens Scudder, 1902. Did the male sing at all and if so, do you remember what the song was like? G. integer is sometimes known as the 'western stutter-trilling cricket' because of its unique stuttering song. You can listen to examples of the song here. If you're interested in Californian field crickets, I'd recommend getting hold of a copy of Weissman et al. (1980: field crickets (Gryllus and Acheta) of California and Baja California, Mexico (Orthoptera: Gryllidae: Gryllinae). Transactions of the American Entomological Society 106: 327–356).

If there were males calling, I don't remember what they sounded like. It sounds like there's no question that this is a Gryllus species though? Eric Eaton had suggested that it was probably something else based on the linked image of the same individual, but obviously this is a clearer shot.

I would go with Gryllus sp. It's definitely not a nemobiine like Eric suggested; Nemobiinae are characterised by the presence of prominent bristles on the vertex and frons and the absence of dorsal spines on the hind basitarsus. In the clearer of your two photos, you can see that the vertex (the area between the compound eyes and antennae) is smooth (no bristles) and dorsal spines are clearly present on the hind basitarsus.

I learned something new today thanks to your detailed comments:-)

It's always helpful to hear specifically what to look for. I've added that information to the Nemobiinae guide page so the information will be easily accessible to others.

Always happy to help! The Grylloidea pages on the guide are in great need of an update. However, it's difficult to know what information is useful as the majority of guide users probably don't have access to a good scope and dissection equipment to examine genital characters or adequate recording equipment to analyse songs etc. This is often the problem with Orthoptera. Eric Eaton and David Ferguson et al. do a great job with the Caelifera and Tettigoniidae, but the grylloid families seem a little neglected.

Yes, certainly the most useful information is the characters that can be seen in photographs. However, it would be useful for all guide pages to note what is required for a complete ID, so that people know what level of ID is reasonable to expect, and perhaps a few would be motivated to start making recordings, etc. I don't currently have the time to pursue that in any comprehensive way, but I always try to incorporate helpful comments such as yours when I come across them.