Complex sentence: From 1879 to 1880, he traveled to Rockerville and Deadwood in the Dakota Territory, to try his hand as local manager for a New York mining company; when the company failed he returned to San Francisco and resumed his career in journalism.
Split into simpler sentences: From 1879 to 1880, he traveled to Rockerville and Deadwood in the Dakota Territory, to try his hand as local manager for a New York mining company. When the company failed he returned to San Francisco and resumed his career in journalism.