A trilateration network extending from near Mammoth Lakes to Bishop, California, was resurveyed following the 23 November 1984, Round Valley earthquake (ML = 5.8). The network had previously been surveyed in 1982. Deformation apparently associated with the Round Valley earthquake was detected as well as deformation due to the expansion of a magma chamber 8 km beneath the resurgent dome in the Long Valley caldera and right-lateral slip on the uppermost 2 km of the 1983 rupture surface in the south moat of the caldera. The deformation associated with Round Valley earthquake suggests left-lateral slip on the north-northeasterly striking vertical plane defined by the aftershock hypocenters located by A. S. Ryall. The earthquake moment implied by the deformation is about 3.8·1017 N-m, a value equivalent to an earthquake magnitude ML = 5.7 in good agreement with the observed magnitude of 5.8. A 0.053 km3 expansion of the magma chamber and 0.32 m slip on the 1983 rupture surface in the 1982-1985 interval was also required to account for the observed deformation.

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