Observation notes: I observed this butterfly while hiking at about 7,500' elevation. There were lots of Pussytoes, Delphiniums, Chickweeds, Phlox, and Dandelions blooming. Also blooming nearby (within a 1/8 mile or so) were Wallflowers (Erysimum spp.)
Verified by: A_baldini
Verified date: August 27, 2018
Coordinator notes: Your hesitant ID is correct. The other similar-looking member of Pierinae in Larimer County, the Olympia Marble, is found in shortgrass prairie habitat at much lower elevations, usually no higher than the base of the foothills (I've seen them right above Dixon Reservoir). Also, the Olympia Marble lacks the "trident" of veining on the bottom right corner of the ventral hindwing.