This year alone, Amazon announced new fulfillment centers in Eastvale, Redlands, Fresno and most recently Sacramento, where the Seattle company said it would hire 1,500 workers.

The warehouses represent a bright spot for cities that have been saddled by a lack of opportunities for less skilled workers. A typical Amazon warehouse job pays $13 or so an hour.

In San Joaquin County, 10,000 new warehouses jobs have helped cut the unemployment rate nearly in half — to a little more than 7 percent — over the last five years, according to research by Jeffrey Michael, director of the Center for Business and Policy Research at the University of the Pacific.

“They’re certainly a big deal for the region,” he said.

Still, the good economic news has been shadowed by questions over the growing role of automation in the retail business.

Amazon says robotic machines work in tandem with humans at its warehouses, rather than replacing them. But the industry is pushing hard to expand the frontiers of such technology, raising doubts not just about warehouse jobs but delivery work that could be made obsolete by driverless cars and drones.