The river flows west from a rugged portion of the central sierra nevada into the central valley and ultimately the sacramentosan joaquin river delta where it empties into the san joaquin rivertogether with its main tributary the. The mokelumne river m e k l em n i or m e k l em i is a 95 mile 153 km long river in northern california in the united states. A fishing weir fish weir fishgarth or kiddle is an obstruction placed in tidal waters or wholly or partially across a river to direct the passage of or trap fish.