Shear‐wave splitting is commonly observed on three‐component microearthquake seismograms recorded at the Northwest Geysers geothermal field, California. The polarization of leading shear waves around each recording station is predominantly N10°–40°E, suggesting that the shear‐wave splitting is caused mainly by pervasive, north‐northeast orientated anisotropy. Time delays between the leading and second shear waves can be as large as 10ms/km to 30ms/km. We propose that the direction and magnitude of this shear wave splitting is due to the presence of pervasive, stress‐aligned secondary fractures related to several northwest‐trending, right‐lateral faults in the Geysers area.