Originally, two large trestles formed a "corkscrew" loop at Spring Canyon, but these were destroyed by a 1976 fire, the smoke from which could be seen from San Francisco. Within six months, a switchback was constructed to bypass the severed loop and the entire line was returned to service. The switchback has an estimated 9.5% grade, making it the steepest passenger grade still in use. The length of the tail tracks in the switchback restricts the trains that may be operated to six cars or fewer. Special events are held to raise funds for repair and reconstruction of the trestles and steam locomotives at Roaring Camp. In 2003, the first "Day Out with Thomas" special event was held. The event was the single largest in the 40-year history of Roaring Camp, with an estimated 25,000 participants over a three-day period.