Now known simply as "The Annex", the former home of the Burien Community Center lies next to the former Crosby Road, now known as SW 146th Street). In the early 1900s, Homer Crosby came to the Highline area and built the road from Ambaum Boulevard to First Avenue South. Crosby, one of the area's early residents, also worked on the construction of Ambaum Boulevard using "donkey engines" to do much of the heavy work of hauling logs, moving earth, and carving out a roadbed.

The Annex property was farm and residential land until Chelsea Park Elementary School was built there. The school was constructed in 1947-48 to relieve overcrowding at Lake Burien, Hazel Valley, and Sunnydale Elementary Schools. The growth of the Highline School District - “favorably known” nationwide - was one of the biggest factors in attracting home-seekers to the South End.