This is C. densus based on examination of the external characters of this female specimen. Based solely on distribution, this should be the subspecies inaequalis but best to leave this at the species level for now as the differences between the 2 subspecies are in the male genitalia.

Note normally shaped front tarsi; Likely Colymbetes densus based on relatively large size and seemingly swollen frons, though hard to judge from the photo- C. incognitus is usually slightly smaller (13-14 mm avg.). There are also 1 or 2 other candidate CA species that I can't rule out based on these images. Like what Brady mentioned, dissection of male genitalia is usually best to resolve species ID in this difficult genus.

Colymbetes sp., yes. There are two common and co-occuring species in the Sierras* (C. densus and C. incognitus). You would need to examine male genitalia among other characters to get a species identification. Gotta love those transverse grooves!

* by which I mean "where the Sierras, Cascades and Great Basin meet", of course.