The Sumas Roundup Association was founded to organize, promote, and raise funds in support of an annual round-up event in Sumas, Washington. Although active from at least 1923-1930, the Association was not formally incorporated until 1927. Its organizers were Sumas businessmen C. M. Eneix, A. W. Linn, C. L. Miller, C. D. Soule and George. I. Dunlap.

The Sumas Roundup itself grew out of a Sumas Junior Rodeo organized in 1923.  The September 28, 1923 edition of the Sumas News noted that over 5000 people attended this event, which spurred the formation and activities of the Sumas Roundup Association.
 

The Sumas Roundup was a major community event. The July 18, 1924 edition of the Sumas News noted construction of a grandstand to seat almost 7000 spectators, while another 2500 could sit in the bleachers. The Sumas News claimed an attendance of over 22,000 people in 1924, and reported that in 1925 there were 12,000 visitors from Canada alone. Although the Roundup's attendance and success continued to grow through 1928, it was cancelled in 1930 following the Wall Street Crash and onset of the Great Depression. The Roundup was re-staged between 1937 and 1940, until its permanent discontinuation due to World War II and lack of finances.

References:
The Sumas News September 28, 1923
The Sumas News July 18, 1924
The Sumas News September 5, 1924
The Sumas News September 11, 1925
Sumas: “A Land Without Trees”
Information supplied by donor, Mike Miller, 2009