Abstract Oligo-Miocene volcaniclastic sedimentation in northern New Mexico occurred before and during initiation of the Rio Grande rift. Reconstruction of dispersal patterns and paleogeography of extensive volcaniclastic aprons, using geochemical, paleocurrent, textural and petrofacies analyses, places important constraints on models for the tectonomagmatic initiation and evolution of the rift. K-Ar ages and chemical analyses of volcanic clasts from conglomerate provide details concerning three primary volcanic centers: 1) San Juan Mountains (29–27 Ma, high-K andesite and rhyodacite); 2) Latir volcanic field (28–25 Ma, high-K andesite and rhyolite); and 3) the previously unrecognized Servilleta Plaza center (23–22 Ma, Iatite, high-K andesite and rhyodacite), which may have been a southern extension of the Latir field. These three volcanic centers provided detritus to the following units, respectively: I) Esquibel Member of Los Pinos Formation, upper Abiquiu Formation, middle Picuris Formation, and Bishops Lodge Member of Tesuque Formation; 2) Cordito Member of Los Pinos Formation and uppermost Abiquiu Formation; and 3) Chama-EI Rito Member of Tesuque Formation and upper Picuris Formation. Correlation of these units is based on both conglomerate and sandstone petrofacies. Detailed point counting of volcanic lithic-grain varieties (vitric, granular, seriate, microlitic and lathwork) is especially useful in discriminating petrofacies. The Esquibel petrofacies has abundant plagioclase, seriate lithics and dense minerals, with low quartz. The Cordito petrofacies has abundant sanidine, quartz and vitric-to-granular lithics, with few dense minerals. The Plaza petrofacies is similar to the Esquibel, but with higher quartz and microlitic lithics, and lower total feldspar and dense minerals. Use of petrofacies simplifies the chaos of stratigraphic nomenclature and allows regional correlations of poorly exposed units. Paleocurrent and textural data from these volcaniclastic petrosomes define volcaniclastic aprons derived from the above volcanic centers. The coordinated use of clast ages and petrology to define source characteristics, sandstone petrofacies to define petrosomes, and paleocurrent and textural analyses to define dispersal patterns provides a powerful method for reconstructing ancient volcaniclastic systems.