Los Angeles County Department of Public Works’ Vertical Control Network is composed of more than 1,700 miles (2,720 kilometers) of level runs and comprise nearly 9,000 benchmarks. The basic accuracy of the net is reflected by an indicated field probable error of ± 0.017 feet per mile (4 mm per kilometer) of leveling as determined from conditions of closure. However, because of varying degrees of subsidence and heaving, the true datum is recovered only by obtaining substantial agreement of a number of benchmarks.For each active benchmark, a point representation was created in GIS by locating them based on their description. Parcel data, mile markers, the County Address Management System (CAMS), LARIAC aerials, oblique photos, 2-foot contour lines and/or Google Street View were used in assisting with the location.The creation of the benchmarks in GIS greatly enhances the Vertical Control Network by adding visual context with respect to their representative geospatial locations. With a glance, geospatial patterns can be observed and out-of-place benchmarks can be quickly identified and remapped to the correct location after verification.To facilitate the adjustment, indexing and distribution of adjusted values in the network, the county territory was divided into 33 quads or areas. For identification purposes, each quad was given a name (for example, “Rosemead”, “La Mirada”, “Santa Fe”, and etc.). Index maps, county maps, and other information can be accessed and downloaded on the basis of each of the quads by going to Survey Division’s Benchmark Retrieval System (https://pw.lacounty.gov/sur/benchmark). General adjustments are carried out every 5 to 10 years and the provided elevation data is expected to remain sound during this period. When a quad is adjusted, new elevations will be published and the date of the readjustment will be noted. No historical data is provided, but it can be acquired from Survey Division’s Public Records Counter or via the fee based Optional Technical Research (OTR) program. For general questions, contact:Hector Chang626-458-7038hchang@dpw.lacounty.govFor survey-related questions, contact:Charles Springstun626-320-9896cspring@dpw.lacounty.govThe following resources can be used to obtain historical benchmark data:PUBLIC RECORDS COUNTER900 S. Fremont Ave, 4th FloorAlhambra, CA 918037:00 AM to 5:00 PM Mon – ThursPhone: (626) 458-5137OPTIONAL TECHNICAL RESEARCH (OTR)7:00 AM to 5:00 PM Mon – ThursPhone: (626) 458-5131