Mast Park in Santee reopened in February 2020 after a ground-up reconstruction at 9125 Carlton Hills Boulevard, adding a nine-hole disc golf course with dual concrete tee pads, a lighted loop trail, and a three-zone off-leash dog park along the San Diego River. The expanded dog area separates small, large, and puppy zones with independent fencing and dedicated water access, flanking the Mast Boulevard corridor where Outliers Jiu Jitsu trains at 10251 Mast Blvd. Gravel riverside trails extend west through riparian habitat along the San Diego River toward Carlton Oaks Country Club, supporting seasonal nesting by the endangered least Bell's vireo. The park's natural-play discovery area incorporates climbable boulders, fallen tree trunks, and drought-tolerant plantings within a Carlton Hills district that also serves pet owners through Hawthorne Country Store Santee on Woodside Avenue. Amenities span a full basketball court, fitness stations with resistance equipment, bicycle maintenance stations, cornhole and ping-pong tables, and reservable picnic shelters with barbecue grills.