Found: small black Lab mix with blue collar

I found this dog this afternoon around 2:30pm in the parking lot behind the Imperial Valley Mall on Imperial Avenue in El Centro. It's a small black Labrador mix, about knee-high, with a blue nylon collar and a white patch on its chest. There's a round tag on the collar with the name 'Rex' and a phone number that I can't quite read from here, and the dog seemed friendly but a bit anxious. I'm hoping to reunite him with his owner—if you recognize him, message me here and we can arrange a safe meet-up near the mall's north entrance.