Complex sentence: In 1935, he left government service to become the special counsel to the president (Ken Kingsbury) of Standard Oil of California (now Chevron) in San Francisco, and began his long career as an oilman.
Split into simpler sentences: In 1935, he left government service to become the special counsel to the president of Standard Oil of California (now Chevron) in San Francisco. The History of Ashland Oil, McGraw Hill, 1968, and began his long career as an oilman.