Write a captivating news report exploring the current landscape of California’s horse racing scene following the collapse of Northern California’s circuits. Highlight the expected changes at Southern California venues like Del Mar, Santa Anita, and Los Alamitos, focusing on the influx of trainers and horses, as well as the potential for larger fields and increased wagering. Don’t forget to touch on the proactive measures being taken to ensure a successful season while addressing any challenges that may arise.