Link for that?
I belong to 3 local AMA sanctioned flying fields here in the Puget Sound but probably 50% of my RC plane flights are outside of the AMA flying fields. A lot of RC Pilots fly at the local soccer fields when they are not in use - there are no formal invitations, Joe tells his buddy Fred, etc., nothing is organized, it just happens. I fly often at one about 5 miles from my house. The closest AMA field is 15 miles away.
Another very popular spot is called "60 Acres" and it is a King County sports park (94 acres total). Not an AMA sanctioned field but almost any day there isn't a game on one of the 25 fields, there are people flying drones, fixed wings, and sail planes. The Soaring club has a sanctioned field, but meet at this field each Wednesday.
Here is a quote from their website:
"The park is divided into two major field areas, 60 Acres North and 60 Acres South. The complex includes twenty-five well-maintained grass fields used for a multitude of sports, activities and special events. 60 Acres was designed to accommodate exhibition games, tournaments, league games, special events, as well as camps and clinics. In addition 60 Acres hosts a variety of passive uses including model airplane flying, rocketry and Frisbee to name a few. Accompanying these fields are paved and gravel parking lots, restrooms, and a covered picnic area. 60 Acres is situated next to the Sammamish River Trail (a popular hiking and biking destination) which connects the Eastside’s and Seattle’s many popular recreational, dining and lodging facilities."
experienceredmond.com