The student pilot departed Van Nuys, CA at about 1530 PDT on a round-robin, cross-country flight to Turlock, CA. It was a combination personal and training flight. His instructor pilot (CFI) had verbally approved the flight, but did not endorse the student's logbook. The student arrived at Turlock at about 1830 PDT. After refueling the plane and having dinner with some friends, he departed on the return flight at about 2000 PDT. After passing Newhall Pass, about 15 mi north of Van Nuys Airport, he observed an overcast cloud condition; however, he could see the valley lights through the overcast. He radioed Burbank Approach Control for assistance. He stated he was not sure of his position. Burbank was unable to radar identify the plane at low altitude. The student did not attempt to proceed to an alternate where VFR conditions existed (as previously instructed by his CFI). He tried continuing thru the overcast and subsequently crashed on a 20 deg rising slope on a westerly heading, in about a 15 deg nose up attitude.