He worked for the Pacific Coast Borax Company, owned by Francis Marion Smith, in Chicago and later at the Death Valley, where Stephen Mather was his boss. He resigned in 1898 and purchased a borax mine in the Frazier Mountain, Ventura County. With Mather, he founded the Thorkildsen-Mather Borax Company. In 1905, he purchased another borax mine in Tick Canyon, a canyon in the Santa Clarita Valley. He became a millionnaire thanks to this second mine. Additionally, he became known as the "Borax King."
He married Dora Garinger. In 1912, they moved into a Craftsman-style estate at the top of Alpine Drive overlooking Coldwater Canyon in Beverly Hills, California. It spanned seventeen acres. A year later, they purchased eleven more acres adjacent to it. They sold it to Kirk B. Johnson, an oilman, in 1921. The house was torn down and subdivided in the 1960s. When he divorced, he moved into an estate in Los Feliz, Los Angeles called Briarcliff Manor, which became known for extravagant parties. He died in 1950.
- Cecilia Rasmussen, 'Borax King' Cleaned Up, but Died Washed Up, The Los Angeles Times, March 12, 2000
- Alan Pollack, Kim Stephens, E. J. Stephens, Legendary Locals of the Santa Clarita Valley, Arcadia Publishing, 2012, p. 39 
- Marc Wanamaker, Early Beverly Hills, Arcadia Publishing, 2005, p. 41