This data set contains three ASCII text files for the Bridger grassland study site in the Rocky Mountains (45.78 N 110.78 W Elevation 2,340 m). Two files contain above- and below-ground biomass data, one for each treatment (ungrazed and moderately grazed). The third file contains climate data from the Big Timber weather station (45.80 N 110.00 W Elevation 1,249 m) near Bridger. Dynamics of above- ... and below-ground plant biomass were monitored by harvest technique at roughly 2-week intervals during the growing season for the years 1970, 1972, and 1973. Data on above-ground live biomass, standing dead matter, and litter are provided for each sampling date. Below-ground biomass (roots and crowns) are provided for 0-30 cm and 0-50 cm depths. Data were collected as part of a coordinated study over 1-3 years at ten grassland sites of the central and western United States under the U.S. Grassland Biome Project of the International Biological Program (IBP). Above-ground net primary production (ANPP) was estimated, conservatively, by summing peak biomass of individual species. Below-ground net primary production (BNPP) was estimated as the sum of positive increments in total root biomass (including root crowns). Values varied according to treatment.