Typically an 80's-90's era Toyota pickup driven by a Hispanic male, piled high with random appliances, towing another similar era Toyota pickup also piled with seemingly random appliances, bicycles, and other items. "IN TOW" is spelled out on the tailgate in duct tape.
These travel in caravans of 3, at a slow speed of 55 mph, usually headed from California to El Paso on I-10, before crossing into Mexico; hence the similarity to the Mayflower voyage.
"Break-1-9, we've got a Mexican Mayflower heading South just past Sacaton."