Coefficients of Conservatism (C-values) are used in Floristic Quality Assessment to evaluate the level of anthropogenic disturbance of a given natural area and exist for much of the United States; however, there is a gap in the southwestern United States. We aim to close this gap by establishing C-values for the flora of the Middle Rio Grande floodplain in New Mexico. We compiled a list of species found in the floodplain (n = 621), and two regional botanists assigned C-values on a scale from 0 to 10 (0 reserved for nonnative taxa and the least conservative native taxa, and 10 being the most conservative). We used correlation analysis to examine the relationship of C-values assigned between botanists as well as shared species between Colorado and New Mexico. There was a significant, but weak, positive correlation between C-values for the two states, highlighting ecoregional similarities and providing a basis of comparison for our C-values. Descriptive statistics indicate the range of C-values assigned are consistent with the disturbance history of the region.