Complex sentence: Attached to Savage's unit was Dr Lafayette Bunnell, the company physician who later wrote about his awestruck impressions of the valley in "The Discovery of the Yosemite".
Split into simpler sentences: Attached to Savage's unit was Dr. Lafayette Bunnell, the company physician. Bunnell later wrote about his awestruck impressions of the valley in "The Discovery of the Yosemite".