Late 1970s, most likely. Too bad the postcard didn't include the crazy looking industrial ruins of the park.
During Norwescon 20 in 1997 at SeaTac the amazing Brad Foster was a guest of honor and several cartoonists hijacked him and took him to this park. I wasn't part of that crew but I did join the subsequent comix lunch. We all compared what we had studied in college to the reality of what we were doing now. I believe I was the only one in the large group who was actually employed in my academic degree (MLS, i.e., librarianship).
