On 11 December 1976 we found an adult Lesser Black-backed Gull (Larus fuscus) standing on the ice at Lake Sangraco, a small sand and gravel borrow area 2.5 km north of Interstate 70 along Lowell Boulevard, northwest of Denver, in Adams Co., Colorado. When first observed it was in a flock of gulls consisting of 15 adult Herring (L. argentatus), 5 adult California (L. californicus) and 50 adult Ring-billed (L. delawarensis) gulls. Later in the week, a first-winter Glaucous Gull (L. hyperboreus) and an adult Thayer’s Gull (L. thayeri) were also present for comparison. The Lesser Black-backed Gull remained at Lake Sangraco through 1 January 1977. This, the first recorded occurrence of the species in Colorado, was also the first record from the deep interior of the United States.