The Sullivan Nature Sanctuary is located on the north side of Platte Landing Park along Rush Creek, west of the bridge entry. The land was donated by members of the Sullivan family and was dedicated in memory of Edgar and Ruth Sullivan, as well as other family members. The North Twin and South Twin trails were named after their twin daughters, Kathryn and Virginia. In honor of Maria Ewing, the matriarch of the Sullivan family, the loop trail at end of the North Wing Trail was named the Maria Ewing Trail in April 2015.
The sanctuary land was part of 8.64 acres acquired from the Brown and Smalley families in 2006 (4.64 acres were purchased and 4 acres were donated). A total of 3.03 acres became dedicated to the Sullivan Nature Sanctuary and the balance was reserved for future parkland. In 2010, the land was platted and the Brown family donated an additional 1.15 acres to the north, expanding the sanctuary to 4.18 acres. In 2014, the Brown and Smalley families dedicated an additional 3.45 acres to expand the sanctuary to 7.63 acres. The remaining acreage is still reserved for future parkland.