No it isn't. A Canadian bulk train 3km long and massing 20 000 tonne at an elevation of 1000m has a potential energy of 20M kg * 9.8 m/s^2 * 1000 m = 196GJ = 54MW-hour. In the winter my house uses about 50kW-hour per day so that will keep about a thousand such houses running for one day. (130m^2, 1950's house, Norway). yes I know my house is not very energy efficient.
A reservoir 10m deep and 45m square at the same elevation has the same potential energy. If you can find a convenient 1000m plateau I think it would probably be cheaper to build a reservoir on top than to build the tracks and trains.