If your MSA is 1300' above the ground, how can you fly at 2000' and be below your MSA?
Because the MSA is calculated on the 5nm either side of track, but you might be competent enough to fly visually right down the middle of the valley?
(Or, I gather, it's usually more polite to fly down the right hand side of the valley, treating the valley's centre line as a "line feature" that you keep on your left.)