Sixteen portable seismograph stations were deployed in the vicinity of the Long Valley geothermal area, California, from April 27 to June 2, 1973. Only minor microearthquake activity was detected in the Long Valley caldera, but a high level of activity was detected to the south and east of the caldera. The abrupt spatial seismicity decrease at the southern boundary of the caldera suggests that the caldera is either structurally less competent than the surrounding crust or is at a junction of different regional tectonic deformation trends. No siginificant attenuation or delays occurred for either local P or S waves that traversed the caldera.