We use seismic waveform cross correlation to determinethe relative positions of 2747 microearthquakes near Mount Lewis, California,that have waveforms recorded from 1984 to 1999. These earthquakes includethe aftershock sequence of the 1986 ML5.7 Mount Lewis earthquake. Approximately 90%of these aftershocks are located beyond the tips of the approximately northstriking main shock, defining an hourglass with the long axis aligned approximatelywith the main shock. Surprisingly, our relocation demonstrates that many ofthese aftershocks illuminate a series of near-vertical east-west faults thatare ~0.5--1 km long and separated by as little as ~200 m. Wepropose that these structures result from the growth of a relatively youngfault in which displacement across a right-lateral approximately north strikingfault zone is accommodated by slip on secondary left-lateral approximatelyeast striking faults. We derive the main shock-induced static Coulomb failurefunction (Δσf) onthe dominant fault orientation in our study area using a three-dimensional(3-D) boundary element program. To bound viable friction coefficients, wemeasure the correlation between the rank ordering of relative amplitudes ofΔσf and seismicityrate change. We find that likely friction coefficients are 0.2--0.6 andthat the assumed main shock geometry introduces the largest uncertaintiesin the favored friction values. We obtain similar results from a visual correlationof calculated Δσfcontours with the distribution of aftershocks. Viable rate-and-state constitutiveparameters bound the observed relationship between magnitude of Δσf and seismicity rate change, and for our favoredmain shock model a maximum correlation is achieved when Δσf is computed with friction coefficients of0.3--0.6. These values are below those previously cited for young faults.