The Cosumnes River (often pronounced ) is a river in northern California in the United States. It rises on the western slope of the Sierra Nevada and flows approximately into the Central Valley, emptying into the Mokelumne River in the Sacramento-San Joaquin Delta. Many locals pronounce the river "kunsumniss," inserting an "n" where there is none in the first syllable. Given the etymological similarity between "Cosumnes," on the one hand, and "Tuolumne" and "Mokelumne" on the other (see next paragraph), a case can be made that the most accurate historical pronunciation is "kasumme," since the "n" is essentially silent in the pronunciation of both "Tuolumne" and Mokelumne," and there is no "s" or "z" sound at the end of those names. An older pronunciation common among Central Valley locals is ), which includes the epenthetic [n] in the first syllable, omits the initial [n] of the final syllable (as in "Molelumne" and "Tuolumne"), has the expected value for the letter in an open syllable (created by the omission of the last [n]), and uses a final [s] rather than a [z].