For the SE Palmdale network in California, triangulation data for the years 1938 and 1958 and trilateration data at about 1-year intervals from 1971 to 1980 are the basis for a strain analysis. A uniform shear strain accumulation over the 40-year period appears to be evident from this data set (&ggr;˙=+0.34¿0.18 μstrain/yr, &psgr;=119¿¿10¿). Previous computations of this coseismic strain change needed further qualification due to the corrupting influence of uncertainties in the network height differences because height differences are critical when triangulation data are compared with trilateration observations. As a result, the height differences of the SE Palmdale network were resurveyed by trigonometric heighting in March 1981. Using these new data, a significant coseismic strain jump related to the 1971 San Fernando earthquake is postulated in the observations. The strain jump can be identified with engineering shearing strains of Δ&ggr;1=+3.3¿1.7 μstrain and Δ&ggr;2=+4.9¿1.7 μstrain or a total shear strain jump of +(5.9¿2.4) μstrain with an azimuth (&psgr;) of 107¿¿6¿ of a line across which right-lateral shear is a maximum. These values are in excellent agreement with those predicted by earthquake displacement models. ¿ American Geophysical Union 1989