While operating a Euclid R-35 end dump EE engaged the retarder & the engine died. This happened while going down ramp into pit & the EE lost control & struck rock wall. The EE said he did not try to apply the brake & because of the model he had no emergency steering. The EE got 3 cuts on his head & 1 cut on his arm & because he was wearing his seat belt his injuries were not worse.