During the second half of the nineteenth century, the introduction of the post office changed daily life in the Western United States. Over the course of 50 years, the number of post offices in this region expanded from just a handful to several hundred. Some post offices were established and stayed in operation long term; others had much shorter life spans as the west continued to change. On this interactive timeline and map, created by historians at Stanford's Center for Spatial and Textual Analysis, visitors can explore a number of post offices that opened and then closed or remained active during any period between 1850 and 1900. Visitors can chose to view this data for durations as short as one year (e.g. data for the year 1873) or for a span of time (e.g. 1880-1892). Once a time period is selected, visitors can view this data via map. This well-conceived project reveals the rapid change of the western United States: for many years, the number of post offices established and closed far exceeded the number of post offices active throughout the year.