We estimate the strike and dip of three fault segments in California (Calaveras, Sargent and a portion of the San Andreas near San Jaun Bautistia) based on principle component analysis of accurately located microearthquakes. We compare these fault orientations with two different first-motion focal mechanism catalogs: (1) The Northern California Earthquake Data Center (NCEDC) catalog, calculated using the program FPFIT (Reasenberg & Oppenheimer, 1985), and (2) a catalog created using the computer code HASH that tests mechanism stability with respect to variations in seismic velocity model and earthquake location (Hardebeck & Shearer, 2002). We assume any disagreement (misfit >30° in strike, dip or rake) indicates inaccurate focal mechanisms in the catalogs. In this way, we can identify which quality parameters best identify well-constrained focal mechanisms. For the NCEDC/FPFIT catalogs we find that the station distribution ratio (STDR) parameter, an indicator of how the stations are distributed about the focal sphere, is the best quantitative discriminator of quality focal mechanisms. Requiring that the STDR>6.5 increases the percent of acceptable mechanisms from 34-37% to 63-68%. This suggests stations should be uniformly distributed surrounding, not aligning, known fault traces. For the HASH catalogs, the fault plane uncertainty (FPU) parameter is the best discriminator, increasing the percent of acceptable mechanisms from 63-78% to 81-83% when FPU≤ 35°. The overall higher percentage of acceptable mechanisms, and the usefulness of the formal uncertainty in identifying quality mechanisms, validates the HASH approach of testing for mechanism stability.