We investigate upper crustal heterogeneity in the western Great Basin and adjacent areas of the Sierra Nevada by simple Pg travel time tomography. We calculate delays between Western Great Basin Seismic Network automatic and analyst picks, and times along straight rays through a 1-d velocity model. To back-project, we distribute the delays into the blocks along the raypaths. Our study area covers a 450 by 750 km, NW-SE trending region using 5 km blocks. To obtain the 1-d velocity model we regressed about 150,000 travel time picks from about 6500 events over three segments of the time-distance curve. The regression gives a surface velocity averaging 5.5 km/s, a Pg velocity of 6.0 km/s, and a Pn velocity of 7.85 km/s. Azimuthal analysis of Pg delays does not reveal any indication of anisotropy. The tomography as a first step computes source and receiver corrections in source and receiver bins normalized by the number of rays; and as a second step back projects delays corrected by the source and receiver delays. By using 70,871 good quality picks from 5064 events with a minimum 10 picks per event, we obtain a regional Pg delay map. A low-velocity patch around the Long Valley caldera is the most consistent structural heterogeneity we map. We verify the validity of our simple method by back projecting the response of a point anomaly at a location with moderate ray coverage. The test shows a good-quality ray set generally over regions linking the Double Spring Flat, Long Valley, Eureka Valley, and Little Skull Mountain seismic areas. This ray set is good enough for efficient recovery of general features from a large dataset of mixed quality picks.