The real influx came in 1848, when a gold strike on the American set off the California Gold Rush. Within one year, the population of the San Joaquin Valley increased by more than 80,000. The city of Stockton, on the lower San Joaquin, quickly grew from a sleepy backwater to a thriving trading center, the stopping-off point for miners headed to the gold fields in the foothills of the Sierra. Rough ways such as the Millerton Road which later became the Stockton - Los Angeles Road quickly extended the length of the valley, some following old cattle routes and Native American trails, and were served by mule teams and covered wagons. Riverboat navigation quickly became an important transportation link on the San Joaquin River, and during the "June Rise", as boat operators called the San Joaquin's annual high water levels during snowmelt, large craft could make it as far upstream as Fresno. During the peak years of the gold rush, the river in the Stockton area was reportedly crowded with hundreds of abandoned oceangoing craft, whose crew had deserted for the gold fields. The multitude of idle ships was such a blockade that at several occasions they were burned just to clear a way for riverboat traffic.