The magazine and story told in this movie are real and true. When Dr. Jess Rodgers (Hans Conried) is explaining how it is possible that the Monsters came into existence suddenly in the Salton Sea, he shows a Life Magazine dated October 17, 1955. This magazine actually had an article about fresh-water shrimp that suddenly appeared in a once-dry Mojave desert lake. David Duncan had read the article when it was first published and used it as the basis for his screenplay.
In prehistoric times the Salton Sea area was an empty desert sink nearly as far below sea level as Death Valley, or a lake (Lake Cahuilla), depending on the course of the Colorado River at the time; the modern-day Salton Sea originally formed in 1905-07 from a pre-Hoover Dam flood of water from the Colorado River. The 1931 project that created Hoover Dam (aka Boulder Dam) was the result of flood control on the river. Eventually becoming the largest lake in California, a boom town grew around the lake, with all the typical real-estate promotional development and hype, peaking in the 1950s. In the ensuing decades, as the lake slowly began to shrink, land values dropped, tourism faltered, the salinity of the water and pollution have increased, and the area has become a virtual ghost town.
The monster appears to be a greatly magnified hellgrammite (a Dobsonfly larva} or the larva of an aquatic beetle, probably a member of the Hydrophilidae. Many of the shots show the fearsome jaws that these creatures have, as well as segmented bodies. They do not look like "molluscs" at all.
In the early scenes in the radio shack, a poster is seen on the back wall. It is a 1954 ad designed by Jan Lavies for the Dutch airline KLM for the resort of Scheveningen.
In the laboratory, above the filing cabinets on the right, is an aerial picture of the K-25 plant, the largest building in the Manhattan Project. It was authorized in late 1942 and was 11 miles from the WWII "secret city" of Oak Ridge, TN. The plant was intended to produce enriched uranium. The photo on the left appears to be a closeup of K-25.