Guaymas (gwī´mäs), city (1990 pop. 87,484), Sonora state, NW Mexico, on the bay of Guaymas. A port on the Gulf of California, it is also the outlet for Hermosillo. Guaymas stands on a scenic inlet girt by desert mountains. Its fine beaches, excellent deep-sea fishing, and transportation facilities have made it a popular tourist resort. In addition to its role as a commercial center for the surrounding region, Guaymas has a substantial fishing industry. Although the surrounding area was explored as early as 1539, the city was not established until the early 18th cent. by Jesuit missionaries. U.S. forces occupied Guaymas in 1846, during the Mexican War, and it was held by the French in 1865–66.