Wikipedia he was born into a family of successful photographers and as a young man moved to Salt Lake City and began his own photography business. In 1901 he married Florence Newcomb, a photographer as well. They traveled around Utah taking photos with a team of mules pulling a homemade darkroom. If you look closely in the lower right hand corned you can see the Hartsook embossment which matches the Hartsook name in the copyright image below.
Eventually they settled in California where he opened studios in a number of cities including Los Angeles and San Francisco. His clients included Mary Pickford, Charles Lindbergh, Lillian Gish and President Woodrow Wilson. I've looked at hundreds of Google images and have half convinced myself that this could be Mary Pickford.
In 1919 Hartsook remarried Bess Hesby and they honeymooned in the redwood forest of Humboldt County, CA. They eventually purchased their honeymoon cabin and 37 surrounding acres turning the cabin into the Hartsook Inn where many Hollywood celebrities stayed including Mary Pickford and Bing Crosby. A forest fire burned down the inn in 1927 and in 1928 the photographic business went into receivership and was sold at auction. Fred died on 30 Sep 1930 at age 53 of a heart attack. His wife would live for another 46 years.