'Filling in Secret Town trestle" Central Pacific Railroad

From the cprr.org site: "Twelve years after the original construction, the great curved Secret Town trestle (the largest structure of its type on the railroad) was completely buried and the valley filled in with dirt from the mountainside by Chinese laborers! This was done to eliminate the fire hazard and avoid replacement of the aging timbers. The Southern Pacific Bulletin later reported that: "a large force of Chinese laborers [was] kept busy during the summer of 1877 making the fill across the canyon to replace the hastily constructed trestle. The trestle was 1100 feet long and 90 feet high and was constructed over the divide between the American River and Bear River when the original lines of the Central Pacific were being extended over this section of the Sierra Nevada Mountains during the spring of 1865."