Large Darkling beetle, 2.5-3 cm long, with pointy hind end.

Coelocnemis magna is a member of Darkling Beetles (Family Tenebrionidae). It is a plant-eating beetle.

BugGuide: https://bugguide.net/index.php?q=search&keys=Coelocnemis+magna

Cucujiform Beetles (Infraorder Cucujiformia)
Taxonomic chart of Cucujiform Beetles. Cucujiformia is an infraorder of polyphagan beetles that represent most plant-eating beetles. https://www.inaturalist.org/taxa/372852-Cucujiformia

The infraorder contains the 7 superfamilies:

Chrysomeloidea (~7 families including longhorn beetles and leaf beetles)
Cleroidea (checkered beetles, bark-gnawing beetles and soft-winged flower beetles)
Coccinelloidea (15 families, includes ladybirds and fungus beetles)
Cucujoidea (~27 families)
Curculionoidea (~8 families primarily consisting of weevils and also including snout beetles and bark beetles)
Lymexyloidea (ship-timber beetles)
Tenebrionoidea (formerly "Heteromera") (30 families including DARKLING Beetles, blister beetles and ant-like beetles)

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NOT

Eleodes gigantea is a large (3-3.5cm long), relatively narrow, all black beetle with a pointy hind end in the Darkling Beetles (Tenebrionidae) family. It is a plant-eating beetle.
BugGuide: https://bugguide.net/index.php?q=search&keys=Eleodes+gigantea

Desert Stink Beetles (Genus Eleodes) Eleodes is a genus of Darkling Beetles, family Tenebrionidae. "They are commonly known as pinacate beetles or desert stink beetles. They are endemic to western North America, with many species found in the Sonoran Desert. They are found in sandy environments. The name pinacate is Mexican Spanish, derived from the Nahuatl (Aztec) name for the insect, pinacatl, which translates as "black beetle." Eleodes species range from 8 to 40 mm in length and are black. All produce an irritating substance as a deterrent to predators, and many will stand on their heads to spray it." https://www.inaturalist.org/taxa/53817-Eleodes