From Saylor(1945) this is a male, since the length of the flabellate club is equal to that of the funicle (= antennal segments 3-6 here).

Using the key to Dichelonyx in Saylor(1945) this goes to D. fulgida crotchii via the characters:

• thorax lacking median longitudinal sulcus;• antenna 9-segmented;• clypeus with rounded anterior corners, not entirely black, without lateral margins narrowing basally, and anterior margin only mildly-reflexed;• elytra bright green, with a (very) narrow pale (testaceous) margin;• terminal segment of maxillary palpus widened apically;• western U.S. locality;• hind angles of thorax obtuse, broadly rounded;• male clubs testaceous;• legs testaceous; elytra elongate (more than 3 times the length of the thorax).
Ths male is also in excellent agreement with Saylor's discussion of D. fulgida crotchi. In particular: it was found in a montane, fir-filled, Sierra Nevada forest; has thorax rather densely hairy; and elytra bright, light-green.

Note that Horn's original 1876 description of D. crotchii was at the full species level, and Fall(1901) treated it as a species as well. This male also keys well to that species in their descriptions, and fits their discussions thereof. Saylor(1945) assigned D. crotchii Horn to subspecies status under D. fulgida LeConte.

It should be noted that nearly all the above pre-1970's authors, upon studying large series of specimens, commented on the variability and intergradation that can occur among various individuals of D. fulgida, D. backii, and D. crotchii...and often their keys had multiple pathways for arriving at the same result for some of these taxa (e.g. allowing for different thorax color, hind margin sharpness, etc.).

In light of that, it's not that surprising that both Hatch(1)(1971) and Cornell(1972) treated D. fulgida crotchi as a synonym under D. backii...and the male here indeed keys to D. backii in each of those works. However, the 2009 catalog of New World Melolonthinae by Evans & Smith(2) recognizes D. fulgida crotchii...and apparently BugGuide currently follows that work.