Most dams don't make good waterfalls but Redridge Dam is an exception. The main dam is a huge steel one that towers above Salmon Trout River, a historic landmark, a dam that no longer holds back any water. Behind the steel structure the original timber crib stands, a modest collection of logs and earth that still holds back a rather large reservoir, and the water pours over and through the wood to form a wide set of cascades.
The most direct drive is along Canal and Liminga Road, although a pretty alternate route down the Covered Road is a great side trek. Head down Canal Road off of M-26 in Houghton, a half mile up from the bridge, and follow it for 4.2 miles to Schmidt's Corner Bar. Turn left on Liminga Road for 6 miles, just past the steel dam to your left before parking on the sandy turn-off on the left side of the road. If you decide to take the scenic option then turn on Cole's Creek Road, a few miles from Houghton, and take that to Covered Rive and turn left on Liminga.
From the parking area follow the sandy drive up and around the dam. If you want to head down to the water right away, past the plaque, you can but there is no good way through the steel dam. You'll need to get over it, either by following the sandy drive to the right or attempting a more direct climb. Once on the far side just follow the drive and paths down to the water. The falls are located upstream a few dozen feet upstream of the steel dam.