The source mechanisms of the three largest events of the 1980 Mammoth Lakes earthquake sequence have been determined using surface waves recorded on the global digital seismograph network and the long-period body waves recorded on the WWSSN network. Although the fault-plane solutions from local data (Cramer and Toppozada, 1980; Ryall and Ryall, 1981) suggest nearly pure left-lateral strike-slip on north-south planes, the teleseismic waveforms require a mechanism with oblique slip. The first event (25 May 1980, 16^h 33^m 44^s) has a mechanism with a strike of N12°E, dip of 50°E, and a rake of −35°. The second event (27 May 19^h 44^m 51^s) has a mechanism with a strike of N15°E, dip of 50°, and a slip of −11°. The third event (27 May, 14^h 50^m 57^s) has a mechanism with a strike of N22°E, dip of 50°, and a rake of −28°. The first event is the largest and has a moment of 2.9 × 10^(25) dyne-cm. The second and third events have moments of 1.3 and 1.1 × 10^(25) dyne-cm, respectively. The body- and surface-wave moments for the first and third events agree closely while for the second event the body-wave moment (approximately 0.6 × 10^(25) dyne-cm) is almost a factor of 3 smaller than the surface-wave moment. The principal axes of extension of all three events is in the approximate direction of N65°E which agrees with the structural trends apparent along the eastern front of the Sierra Nevada
