 
|
2 to 24 Million
Years Ago – Geologic record indicates Wash floodplain development
The Las Vegas Wash floodplain was initially formed roughly two to 24 million years ago, as a result of
filling of the Las Vegas Valley by sediments that were deposited by erosion of surrounding ranges
and higher elevations. The majority of these sediments consist of easily eroded silts and clays
with minor amounts of sand and gravel. Geologic evidence indicates that the Wash has undergone
at least three natural cycles of down-cutting and subsequent back-filling prior to modern
development. The Wash became a tributary to the Colorado River about three million years ago.
For the last few hundred years, the Valley
has been a source of water in the dry Mojave Desert. Meadows, or wetlands, were supported by a
spring complex known as the Big Springs, located in the central
part of the Valley. Las Vegas Creek was formed by these springs and flowed through the Valley,
percolating into the ground water system prior to entering the lower portion of the Wash. The
lower part of the Wash was ephemeral with the exception of a small spring and wetland area
near what is now known as Three Kids Wash.
Early
1900s – Modern settlers make Las Vegas home resulting in increased water flows into the Wash
At the turn of the century, the Wash was, for the most part, an ephemeral stream, carrying
storm flows to the Colorado River. A few mesquite were present in the Wash, as well as a
small wetland located at a spring just above what is now know as Three Kids Wash. Flows
in the Wash measured prior to 1928 recorded perennial flows of one cubic foot per
second (cfs).
Flows in the Wash increased proportionally
with population expansion in the Valley. Modern settlement followed construction of the railroad
linking Salt Lake City, Utah, with Los Angeles, California, in 1905. The Valley grew at unprecedented
rates during construction of Hoover Dam in the 1930s, World War II related activities in the 1940s,
and accelerated growth of the gaming and entertainment industry in the 1950s. Since then, a steady
and increasing immigration of residents to the Valley has caused flows in the Wash to permeate and
moisten the floodplain, transforming its vegetation from a sparse, desert-shrub community to a
greenbelt that included ponds and wetlands. This progressively increasing floodplain saturation
caused the Wash to begin flowing continuously in 1955, a drastic change in the hydrologic
regimen from the previous 2,500 years.
|
|
