Saturday’s California Derby at Golden Gate Fields is a stepping-stone to next month’s Grade 3 El Camino Real Derby, but it’s hard to envision a better stakes race being held here this year. The $100,000 1 1/16-mile race drew a full field of 12 runners, seven of them coming off a victory. The favorite is likely to be Positive Response, who has won two straight races at a mile, including a six-length score in last month’s Gold Rush. Dancing At Dark brings a two-race winning streak into the California Derby, his stakes and route debut. The Great Caper, Zayda, Bluegrass Reward, Jakesam and Cut Fastball are coming off a victory. Grand Maneuver ran second to Positive Response in the Gold Rush after winning a one-mile allowance race on the turf. Jakesam, Mazarron, and Grand Maneuver have each won at Saturday’s distance. This is the time of year when young 3-year-olds can make overnight improvements, and trainer Billy Morey believes Positive Response is a better colt going into the derby than he was going into the Gold Rush. “The horse is doing really well,” Morey said. “I think he’s improved on his own. He’s training better up to this race than he was training for the Gold Rush.” Although he’s the only stakes winner among the dozen entrants, Positive Response is meeting the toughest challenge of his career. But this is the type of challenge Morey envisioned when he, Saul Gevertz, Roger Newman and Ray Pagano paid about $75,000 for the gelding. “This is the best stakes series we have here,” Morey said. “One of the main reasons we bought him was our hope he’d be a good fit in races like this. But I didn’t expect him to win the [Gold Rush] by six.” Julien Couton rode Positive Response in the Gold Rush, and will be aboard again on Saturday. Couton entered this week tied with Russell Baze atop the Golden Gate Fields jockey standings. Couton had never been aboard Positive Response before the Gold Rush, which was the jockey’s first stakes win. He has been working the horse since then. Although Morey is happy to have Couton back on Saturday, he said Positive Response is easy to get along with. “He is easy to train and has no real quirks, but it’s obvious the horse-rider relationship is important in big races,” Morey said.