Michael Portillo is nearing the end of his thousand-mile rail journey from Reno, Nevada, to San Diego in southern California. In this final leg, clad in khaki boiler suit and sporting dark glasses, he joins the US Navy Pacific Fleet, birthplace of the elite flying academy Top Gun. Aboard the Pacific Surfliner, he arrives first in the coastal town of La Jolla, where he takes to the water in a kayak to explore the extraordinary 75-million-year-old caves. In San Diego, he picks up the trail of the industrialist and property speculator John D Spreckels, who made the city boom in the 19th century and built a pavilion to house the largest outdoor pipe organ in the world. Michael is offered the chance to play it. Appleton's recommends a trip to a huge structure, completed in 1888, on which San Diegans have depended for water for 130 years - the Sweetwater Dam.