Long ago, the Colorado River flowed through country so flat that
its course constantly changed as silt deposits blocked its flow.
At times, the river flowed into the Gulf of California, while at
other times it headed west into a low lying area called the
Salton Sink. Each time the sink filled with river water, a large
lake formed. This lake was called Lake Cahuilla. It covered over
100 miles, stretching from Palm Springs southward into Mexico.
Each time the river changed its course from the sink to the Gulf
of California, the lake dried up, leaving behind miles of sandy
beaches. Northwesterly winds blew across the dry lake bed and
swept the sandy beaches to the southeast. Eventually, the sand
piled up on itself and formed dunes. What stops the dunes from
blowing further south?