I Googled it and found something that said there are still visible remnants of it out South Street at Meadow Park. I don't know how old the information I found is and it is likely a shopping center now? LOTS of changes since the 1920's. Also, Ralph DePalma evidently set a world speed record at the SLO track.
No shopping center out there yet and doubt there ever will be. If you googlemap it, you can see a relatively new housing track (compared to other houses across the street around the school). The brown part in the park is a new garden that they put in within the last 2 years. I've only wandered around the park a little but don't recall seeing anything that looked out of place for a park. *shrug*