A topological graph, or quiver, is a directed graph where the edge and vertex spaces are topological spaces. The C*-algebra associated with the graph is a Cuntz-Pimsner algebra of an associated C*-correspondence over an abelian C*-algebra. For a given graph satisfying a properness hypothesis we construct and abstractly characterize a subgraph containing the iterative dynamical core of the original graph. The C*-algebra of this subgraph is a quotient of the C*-algebra of the graph, and under some additional assumptions is a crossed product C*-algebra by a shift endomorphism. This is accomplished using a composition product of topological graphs.