Im pretty sure that like 90+% of all lettuce produced in the US is grown in Yuma, AZ

Edit: I just looked it up and yes that is correct. In fact, between Yuma and the Salinas Valley in California they grow over 90% of all leafy greens that are consumed in the US. So its definitely safe to eat just about anything that isnt Taylor Farms iceberg that was grown in Mexico specifically. Or at least as safe as eating lettuce ever is