Prince Charles and his wife, Camilla, took their royal tour of the United States to northern California on Saturday, examining local produce at a market and lunching with locals at an organic farm near San Francisco.

The prince and Duchess of Cornwall will spend more than three days in the region as the trip shifts from the power centers of New York and Washington to more rural areas and issues close to the prince's heart — organic agriculture and sustainable food production.

The prince is a firm supporter of environmental causes and runs an organic farm on his Highgrove estate in England. He also has a multimillion-dollar line of organic foods, Duchy Originals, whose profits go to charity.