Matt McGuire, general manager for Yuma-based JV Farms, acted as tour guide, offering an overview of the region's history as it evolved into the United States' winter vegetable capital, including the role of the farmworker strikes led by Cesar Chavez in the 1960s and '70s in driving winter vegetable production into Arizona.

"He really did accomplish a lot of good things. The farmworkers weren't treated very well, and they weren't paid very much in those days, McGuire said.

Despite higher consumer interest in fresh produce these days, McGuire said overall lettuce consumption is relatively flat, though romaine and spring-mix varieties are taking a bigger cut of the total market away from iceberg.

But the rise of big retail customers such as Walmart has created large contracts with big expectations in both quantity and quality, including the dimensions of the produce for shipping and resale purposes, so growers and shippers sometimes have to turn to other suppliers.

"There are more hard contracts, less act of gods," he said, forcing suppliers to turn to other sources.

"They'll buy whole fields of lettuce from the carton guys, because that's the only place they're going to have it. They'll open their pocketbook and they'll buy that field. If they can't buy a field, they'll buy all the cartons on the open market that they can find. Because they got a contract."