The Potomac River meanders through six miles of bends here, with steep cliffs dropping to the river and making the digging of a ditch canal nearly impossible. The canal company could have followed a natural fold in the rock stratification to burrow the tunnel, but this would have taken them too far from the river. They instead tunneled a short distance diagonally through the rock folds, a decision that led to many cave-ins because of the predominate soft shale they encountered. The river and the rocks here were unforgiving, costing the canal company time and money in its race with the railroads.