The population of California exploded so rapidly as a result of the gold rush, that by 1850 it had met statehood qualifications and was admitted into the Union as the 31st state. On this map, San Francisco is connected to Chicago and Jefferson City by a thick dashed line, which represents the proposed route for the "Great Pacific Railroad," which is explained further in the note just above the bottom margin.
An interesting aspect of this map is its attempt to detail the various natural curiosities found in the west. One of the more interesting notes on this map the description of The Bad Lands as "a Region abounding in Fossils." Another indicates the location of an unnamed volcano reported to be "in a state of eruption."
Before there was an operating transcontinental railroad, the need for swift mail service between the east and California led to the creation of the Pony Express Route, which is marked on this map by a double line leading from St. Joseph to Sacramento. Pony Express Riders were able to deliver messages in ten days, which was remarkable considering the same route would take months by wagon. When the first transcontinental telegraph was completed in 1861, however, messages could be deliver in minutes rather than days, rendering the Pony Express obsolete less than two years after its creation. The short time span of the Pony Express ensures that only a few maps -- those published in 1860 and 1861 -- fully depict its route.
As more western states were admitted into the Union, the issue of slavery was pushed to the forefront of the political scene. The southern slave states felt threatened each time a new state was admitted as "free" rather than "slave," and eventually resorted to succession and war to postpone the inevitable prohibition of slavery. This map illustrates the South's concern with the newly organized territories highlighted in bright green.