The results of levelings along U.S. Highway 395 between Lee Vining and Toms Place, California, in 1957, 1975, 1980, 1982, and 1983 define the development of a dome‐shaped uplift across the Long Valley caldera. These levelings indicate that Toms Place remained virtually invariant with respect to Lee Vining during the full interval 1957–1983, implying that the end points of the survey route lie beyond the range of the developing dome. No significant uplift occurred before 1975, but by October 1980 the uplift near Casa Diablo Hot Springs reached 0.25 m and the half width of the dome was of the order of 25 km. The uplift of Casa Diablo Hot Springs increased to 0.35 m by August 1982 and to about 0.40 m by August 1983 without any appreciable increase in the lateral extent of the dome. The August 1982 to August 1983 uplift apparently occurred before February 1983 with little or no uplift during the period February–August 1983. The 1975–1983 uplift is attributed to the injection of 0.19 km3 of magma into a spherical chamber at a depth of 10 km beneath the southern quadrant of the ancient resurgent dome within the caldera. Examination of the full vertical control record through the Long Valley area indicates that the 1975–1983 uplift is unique within the period 1905–1983. Although comparisons of the results of a 1932 leveling against a 1914 datum disclose a 1914–1932 down‐to‐the‐northwest tilt of about 10 µrad over the reach between Toms Place and Lee Vining, this tilt (if real) is more reasonably attributed to regional tectonic deformation than it is to the movement of magma at depth.

Annual surveys of trilateration and leveling networks in and around Long Valley caldera in the 1982–1985 interval indicate that the principal sources of deformation are inflation of a magma chamber beneath the resurgent dome and right‐lateral strike slip on a vertical fault in the south moat of the caldera. The rate of inflation of the magma chamber seems to have been roughly constant (0.02 km3/yr) in the 1982–1985 interval, but the slip rate on the south moat fault has decreased substantially. In addition, there is evidence for a shallow source of dilatation (possibly dike intrusion) beneath the south moat of the caldera in 1983 and less certain evidence for a deep source (possibly magma chamber inflation beneath Mammoth Mountain) in the western caldera in 1983–1985. Deformation in the 1985–1986 interval as inferred from trilateration alone seems to be similar to that observed in 1984–1985.

Continued deformation of the Long Valley caldera from the summer of 1983 to the summer of 1984 Is Indicated by resurveys of leveling and trilateration networks. The trilateration surveys can be explained by continued inflation (0.022 km) of a spherical magma chamber located 10 km beneath the resurgent dome plus continued right-lateral slip on the uppermost 2 km of the 1983 rupture surface in the south moat of the caldera. The leveling data suggest a minor upwarping over the resurgent dome but are dominated by a regional tilt (0.9 yrad down to the southeast) over 60 km. Although the leveling data satisfy the usual routine tests for absence of systematic error (e.g., no correlation with topography, satisfactory loop closures, satisfactory agreement between the cumulative sums of backward and forward runs), we are unconvinced that the regional tilt is real. Unusual difficulty in obtaining satisfactory section closures in the double-run sections of the leveling is the primary basis for our skepticism.

Measurements of deformation in and around the Long Valley caldera in the interval July 1983 to August 1984 indicate that deformation is proceeding at a roughly uniform rate and that the net deformation for the year is about the same as for the preceding year. The 1983–1984 deformation of the 40‐line trilateration network can be approximated as the effect of the expansion (0.022 km3) of a spherical magma chamber located 10 km beneath the resurgent dome plus right‐lateral slip (50 mm) on the uppermost 2 km of the 8.5‐km‐long 1983 rupture surface in the south moat of the caldera. This same model furnishes an approximate fit to the tilting observed at six 1‐km aperture bench mark arrays within the caldera, although the quantitative fit lies somewhat outside the estimated observational error. The model, though obviously too simple to furnish a detailed fit to the complex process of magma chamber reinflation, does furnish a reasonable overall picture of the deformation.