We prove a special case of a dynamical analogue of the classical Mordell-Lang conjecture. Specifically, let ϕ be a rational function with no periodic critical points other than those that are totally invariant, and consider the diagonal action of ϕ on (P 1 ) g . If the coefficients of ϕ are algebraic, we show that the orbit of a point outside the union of the proper preperiodic subvarieties of (P 1 ) g has only finite intersection with any curve contained in (P 1 ) g . We also show that our result holds for indecomposable polynomials ϕ with coefficients in C. Our proof uses results from p-adic dynamics together with an integrality argument. The extension to polynomials defined over C uses the method of specialization coupled with some new results of Medvedev and Scanlon for describing the periodic plane curves under the action of (ϕ, ϕ) on A 2 .