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The blues with spotted undersides and orange marginal hindwing bands form a group of similar species, which include the Northern (Lycaeides idas), Melissa (L. melissa), Shasta (Icaricia shasta), and Acmon (I. acmon) blues. Ancilla and acmon are the only species with a dot in the mid-discal area (in addition to the dot at the distal end of the discal cell) of the forewing underside; To further separate ancilla from acmon, look at the wing fringe, which is checkered in ancilla and white in acmon, and the shiny, metallic scales on the hindwing marginal band are absent. The Rocky Mountain Blue was considered to be a subspecies of E. enoptes (Boisduval) until recently (Pratt & Emmel 1998).

No life history information is available for Alberta populations. The larvae vary in colour from pale yellow or white with brown markings, matching the flowers they feed on; pupae hibernate (Layberry et al. 1998). Adults are fast fliers, but stop to perch on the flowers of umbrella-plant and yellow composites (Bird et al. 1995).

As the name suggests, this blue is restricted primarily to the Rocky Mountain region, south to northwestern New Mexico, with a separate population occurring from central Washington to southeastern California (Opler 1999). In Canada, this species is restricted to southern Alberta and southwestern Saskatchewan (Layberry et al. 1998).