Measurements of changes in the distance (or length) between monuments are provided. These measurements were made using a two-color Electronic Distance Meter (EDM) that can measure distances between 1 and 10 KM. Nominal precision of these data range from 0.3 mm to 1.0 mm dependent upon the baseline’s length. These measurements were made between mid-1975 to mid-2006. Data in this archive are from eight networks, each consisting of more the 9 baselines. The locations of these networks in California include far northwestern California, Hollister, CA., Long Valley Caldera in eastern California, Parkfield, Pearblossom, and Anza; the last two located in Southern California. For four of the networks (Hollister, Parkfield, Long Valley, and Pearblossom), measurements were made roughly once per day with the goal of documenting transient deformation associated with earthquake and/or volcanic areas. Measurements of the other networks were less frequent from a few times each year to annual measurements. In many respects, these data, especially those made daily, are a forerunner of the current method of using GNSS receivers being operated continuously to measure deformation. Some highlights from these data include the following: 1) episodes of inflation of the Long Valley caldera including the energetic episode in late 1997; 2) A 20 year record with high temporal resolution of deformation that proceeded 2004 M6 Parkfield earthquake which includes at least one episode of transient deformation; and 3) A 20-year record of steady rate of strain accumulation over a 10 km long segment of the San Andreas fault in Southern California. The two color EDM is unique amongst EDMs. By ranging on two wavelengths (red and blue), it was able to resolve the correction to the optical travel-time to within 0.1 parts per million (ppm) of the length of the baseline. In contrast, the common single-color EDM require measurements of temperature and pressure at the end points of the baseline and a critical assumption that the temperature and pressure are constant along the baseline. At best, the precision of single color EDMs is 1 ppm. Refined-single color EDM measurements employed an aircraft equipped with temperature and pressure sensors to obtain the profile of these quantities along the baseline.
