Answer:
No, most weren't successful. The Sacramento Bee newspaper reported that "one in every five miners who came to California in 1849 was dead within six months." Those who lived to tell the tail found the work very hard. Most of those who became wealthy off gold were (1) lucky and (2) found their gold during the early days of the Gold Rush.
Actually, alot of those who got rich off the gold rush were the ones who ran businesses to support the prospectors' needs for clothing, equipment, etc.