We study anthropogenic noise sources seen on seismic recordings along the central section of the San Jacinto fault near Anza, southern California. The strongest signals are caused by freight trains passing through the Coachella Valley north of Anza. Train-induced transients are observed at distances of up to 50 km from the railway, with durations of up to 20 min, and spectra that are peaked between 3 and 5 Hz. Additionally, truck traffic through the Coachella Valley generates a sustained hum with a similar spectral signature as the train transients but with lower amplitude. We also find that wind turbine activity in northern Baja California introduces a seasonal modulation of 1-to 5-Hz energy across the Anza network. We show that the observed train-generated transients can be used to constrain shallow attenuation structure at Anza. Using the results from this study as well as available borehole data, we further evaluate the performance of approaches that have been used to detect nonvolcanic tremor at Anza. We conclude that signals previously identified as spontaneous tremor (Hutchison and Ghosh, 2017) were probably generated by other nontectonic sources such as trains.Electronic Supplement: Seismograms during a transient, decomposition of the large amplitude signal into sequences of repeating patterns, detection statistics in the two stages of the tremor search procedure, velocity amplitude spectra of transients from two collocated borehole-surface station pairs, median weekday-night spectra for all stations in the Plate Boundary Observatory (PBO) Anza network, time variations of root mean square (rms) velocity for all stations in the PBO Anza network, cumulative population and kilometers of railroad on which the allowed speed for freight trains exceeds 50 mph, envelopes of vertical ground motions as a function of time, vertical ground motions recorded by the Anza borehole stations, and spectrograms of vertical ground motion and corresponding wind speeds.