"The Des Moines Incident" is a UFO encounter that supposedly happened on the water just off Des Moines in 1947. A mural just around the corner for the wedding site commemorates the event, which is the source of the "men in black" UFO mythology.
From Wikipedia:
On June 24, 1947, private pilot Kenneth Arnold reported that he saw a string of nine shiny unidentified flying objects flying past Mount Rainier at speeds that Arnold estimated at a minimum of 1,200 miles an hour (1,932 km/h). Arnold's report garnered nationwide news coverage and his description of the objects also led to the press quickly coining the terms flying saucer and flying disc as popular descriptive terms for UFOs. Ten days later, Capt. E.J. Smith, his co-pilot, and a stewardess reported witnessing unidentified objects in the Pacific Northwest.
On July 29, Arnold interviewed Harold Dahl, who reported:
On June 21, 1947 in the afternoon about two o'clock, I was patrolling the east bay of Maury Island [...] I, as captain, was steering my patrol boat close to the shore of a bay on Maury Island. On board were two crewmen, my fifteen-year-old son and his dog. As I looked up from the wheel on my boat I noticed six very large doughnut-shaped aircraft.

Dahl said that one of the objects "began spewing forth what seemed like thousands of newspapers from somewhere on the inside of its center. These newspapers, which turned out to be a white type of very light weight metal, fluttered to earth". According to Dahl, a substance resembling lava rocks fell onto their boat, breaking a worker's arm and killing a dog.

Dahl said his superior officer, Fred Crisman, investigated the incident. Dahl also claimed he was later approached by a man in a dark suit and told not to talk about the event. Crisman, when interviewed, reported having recovered debris from Maury Island and having witnessed an unusual craft.