sentences:  For use within a mine the overhead wires may occasionally be relocated as excavation activity progresses.Hence the trolleytrucks used in mines do not necessarily have a travel route that is as fixed as the trolleytruck routes used in cities.From 1956 to 1971 the Riverside Cement Company in Bloomington, California, operated Kenworth dump trucks converted to trolleytruck use at the Crestmore Quarry near Riverside, California.