Seven people are killed in the Mussel Slough Tragedy, a gun battle in California.

The Mussel Slough Tragedy was a shootout over disputed land titles between settlers and the Southern Pacific Railroad (SP). It took place on May 11, 1880, on a farm located 5.6 miles (9 km) northwest of Hanford, California, in the central San Joaquin Valley. Seven people were killed. The episode became a major theme in many protests and publications denouncing the railroads as villains in California history.

May 11 is the 131st day of the year in the Gregorian calendar; 234 days remain until the end of the year.