California's western Sierra Nevada had more frequent fires between 800 and 1300 than at any time in the past 3,000 years, according to a 2009 study based upon tree-ring research. Scientists reconstructed the history of fire during this droughty period by dating the years in which fire scars were found in ancient giant sequoia trees in the Giant Forest of Sequoia National Park . The result: These 500 years, known as the Medieval Warm Period, had the most frequent fires in the 3,000 years studied. During this period extensive fires burned through parts of the Giant Forest at intervals of about 3 to 10 years. Any individual tree was probably in a fire about every 10 to 15 years.
Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it.  A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on the project, together with their families.  Another camp, on the flats along the Colorado River, was officially called Williamsville, but was known to its inhabitants as "Ragtown".  When construction began, Six Companies hired large numbers of workers, with more than 3,000 on the payroll by 1932  and with employment peaking at 5,251 in July 1934.  "Mongolian" (Chinese) labor was prevented by the construction contract,  while the number of blacks employed by Six Companies never exceeded thirty, mostly lowest-pay-scale laborers in a segregated crew, who were issued separate water buckets.