In 1956, George Wyse became superintendent of King County Parks, a position he held until 1976. Wyse oversaw the expansion of park use of school facilities and the signing of the first contract with the Highline School District in 1958 for joint park-school use. The Parks Department developed the outdoor facilities at Moshier Park and gained the use of the Highline High School gym (and, possibly, Highline Memorial Stadium) for recreational programs.
The Highline Project at Highline High School was promoted by Associated Clubs of South King County. Bill Moshier of Shorewood was active in this group and influential in developing the plan for the extensive array of ball fields. When Bill died suddenly, Moshier Field was named in his memory. Moshier served as a King County Commissioner in 1958, and was one of the initial members of Metro's 15-member governing Council.
In 1962, King County established the first county arts center and year-round arts program at William Moshier Memorial Park. Between 1962 and 1972, the Center was redesigned to accommodate pottery and jewelry programs.
In 1968, King County voters approved Proposition 6, a Forward Thrust Parks and Recreation bond, which included $39,400 for facilities improvements at Moshier Park. The Moshier complex included three lighted softball / baseball fields, one lighted 90-foot softball / baseball field, two lighted football / soccer fields, and a public restroom.
Moshier Park was one of nine King County Parks in Burien that was transferred to the City in 1994.