These data were compiled for a study that investigated the effects of drought seasonality and plant community composition in a dryland ecosystem. In 2015 U.S. Geological Survey ecologists recorded vegetation and soil moisture data in 36 experimental plots which manipulated precipitation in two plant community types. The experiment consisted of three precipitation treatments: control (ambient precipitation), cool-season drought (-66% ambient precipitation November-April), and warm-season drought (-66% ambient precipitation May-October), applied in two plant communities (perennial grasses with or without a large shrub, Ephedra viridis) over a three-year period. These data were collected from 2015 to 2022 near Canyonlands National Park, UT. These data represent precipitation, soil moisture, percent cover estimates, soil biogeochemistry data (carbon, nitrogen, and phosphorus concentrations) and biomass from experimental treatments. The datasets includes data on when treatments were imposed, ambient precipitation, soil moisture measured at two depths, plant cover and plant biomass measured in the spring and fall from 2015-2019. Additionally, soil cores were collected in the fall 2018 and spring 2019 to measure biogeochemical cycling concentrations for available carbon, nitrogen, phosphorus, and microbial biomass. Standing grass biomass and Ephedra viridis biomass are done through allometric relationships based on a combination of point-frame green hits, leaf lengths, and leaf numbers, combined with double sampling. The biomass data provide an estimate of how treatments are impacting overall grass and shrub species productivity. These data can be used to compare the effects of drought seasonality on shrub and grass communities and biogeochemistry dynamics.