A proof that strong solutions of the Dullin–Gottwald–Holm equation vanishing on an open set of the (1 + 1) space-time are identically zero is presented. In order to do it, we use a geometrical approach based on the conserved quantities of the equation to prove a unique continuation result for its solutions. We show that this idea can be applied to a large class of equations of the Camassa–Holm type.