Colias eurytheme, the Alfalfa, can be found in numerous states in every region of the country.
Favorite nectar plants include: Asclepias and Lantana
USDA Growing Zones for these plants include: 3,4,5,6,7,8,9,10

Host plants:
Arachis hypogaea
Astragalus alpinus
Astragalus bisulcatus
Astragalus crassicarpus
Astragalus crotalariae
Astragalus drummondii
Astragalus flexuosus
Astragalus plattensis
Astragalus racemosus
Astragalus trichopodus phoxus
Astragalus whitneyi
Astragalus
Baptisia
Cassia
Coronilla
Cucumis melo
Glycine max
Glycyrrhiza lepidota
Lathyrus jepsonii californicus
Lathyrus lanszwertii leucanthus
Lespedeza
Lotus crassifolius
Lotus grandiflorus
Lotus scoparius
Lotus strigosus
Lotus unifoliatus unifoliatus
Lotus wrangelianus
Lupinus bicolor
Lupinus minimus
Lupinus perennis
Lupinus succulentus
Medicago lupulina
Medicago polymorpha
Medicago sativa
Medicago
Melilotus officinalis
Phaseolus
Pisum sativum
Psoralea
Sesbania herbacea
Thermopsis rhombifolia montana
Trifolium longipes
Trifolium nanum
Trifolium pratense
Trifolium reflexum
Trifolium repens
Trifolium stoloniferum
Trifolium willdenowii
Trifolium wormskioldii
Trifolium
Vicia americana
Vicia cracca
Vicia sativa nigra
Vicia sativa
Vicia villosa
Vicia

PD images courtesy of:
unknown
USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA
USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA
USFWS midwest

CC 2.0 images courtesy of
Kristof Zyskowski & Yulia Bereshpolova
Cristina Butler
Judy Gallagher
Judy Gallagher
Judy Gallagher
Judy Gallagher
Michael Mulqueen
Bettina Arrigoni