Trestle bents were usually around 16 feet apart, and on one end, the left over length was covered. Example, if you had a 60 foot bridge, there would be 3 spans at 16 feet, and one at 12 feet. Steel bridges and truss bridges were different...
Trees were very sparse in the early days, lumber that was usable was cut down for ties and other in the immediate area. Later on, vegetation grew back, but the D&RGW in this area has been gone almost as long as it survived. This means the trees and plants have had twice as long to grow as the railroad survived...
Casey