Rest assured, Blaine, when it comes to ID efforts I'm very much in the careful, thoughtful, and detailed reasoning camp...although that doesn't mean I don't get things wrong at times! :-)

While I agree that field guides are generally not sufficient for definitive ID's...they *can be* good for formulating likely candidates. Before posting the series here, I tried but was unable to find the 1945 revision by Saylor online (cited on info page here). (I found some of the older Bull. Brooklyn Ent. Soc. issues at BHL, but not beyond 1923). [Saylor(1945) has since been made available: key here, discussions of D. valida and D. vicina here.]

However, today I did find an earlier treatment of the genus (under the name, Dichelonycha) written by H. C. Fall in 1901. Even though it's quite old, the key in Fall's paper (available here), treats (up to synonymy) all but five of the 28 species listed in the 2005 checklist of New World chafers by Evans & Smith. The missing species in Fall's key are: D. crumbi Hatch 1971, D. kirbyi Brown 1946, D. oregona Van Dyke 1918, D. testaceipennis Fall 1907, and D. vandykei Saylor, 1932.

Regarding the species in my area: Evans & Hogue(1) state there are 15 species of Dichelonyx in CA (see pg. 114 here). Consistent with this, a search for "Dichelonyx" on the California Beetle Database yields 15 species. D. vandycki is the only species on the CA list that isn't covered in the 1901 key of Fall (again, up to synonymy).

The individual in my photos is "sulcate", i.e. it has a deep longitudinal groove on the pronotum. Among the species covered by Fall, only 5 on the CA list are sulcate: decolorata, lateralis, pusilla, valida, and vicina. From Fall's key, if this is a male, then characters for the hind tibial spur and elytral color appear to eliminate the first three of these (see comments with 5th image in this series...also compare with the MCZ type images of pusilla and decolorata).

My best effort at interpreting Fall's key for the post here leads me to D. valida. Having said this...I must add that among all the MCZ type images, to my eye the images for D. lateralis are perhaps the best match for my specimen, including the two other top contenders: D. valida and D. vicina. In making this comparison, I'm considering the overall ratios of length and width of the elytra to thorax & head; the shape of the pronotum (including size and placement of the lateral angles); the pale clypeus; and the color and pattern of the elytra.

However, the discussions in the 2006 guidebook by Evans & Hogue(1) and the book by Furniss, Carolin, & Keen(2) use the name "Dichelonyx valida vicina" and seem to indicate that it is among the more widely distributed and commonly encountered taxa in coniferous montane habitats of CA. The use of the trinomial "Dichelonyx valida vicina" makes me wonder whether the two taxa D. valida and D. vicina are considered synonyms, even though they were listed as separate species in the 2005 checklist here. In support of this hypothesis, the California Academy of Sciences general collection database lists 51 out of 150 CA Dichelonyx entries under the species name "D. valida", including 30 entries under subspecies D. valida vicina and 7 entries under D. valida lateralis. They have none under species D. lateralis. Similarly, the collection record numbers on the California Beetle Database web site list 60 records for D. vicina, just 1 each for valida and vandykei, and 0 for lateralis! Of all those records from both sources, the Kings Canyon National Park location here is within the implied the range of D. (valida) vicina only.

So...I still don't have a unequivocal ID, but I'm down to "3" candidates (two, or maybe even all(!), of which might be considered synonyms?) and the wild card D. vandykei. In terms of collection records and implied abundance vs. rarity in the discussions in Evans & Hogue(1) and Furniss, Carolin, & Keen(2), it seems "D. valida vicina" is the most likely. Perhaps someone knowledgeable with the genus, and ideally with access to Saylor's 1945 treatment and a specimen collection, could finish off the process without too much difficulty?