While in college, Hagerman took a job as a clerk with the Milwaukee Iron Company, a manufacturer of railroad ties.

Hagerman built the nearby town of Norway, Michigan, to provide housing and services for the company's employees.

Hagerman sought to expand the railroad to Aspen and Grand Junction, and possibly west to Utah.

Hagerman also used lucrative coal mines to not only power his railroad but also to sell coke to the Leadville smelters.

Seeking capital to purchase these properties before news of the strike got out, Gillespie contacted Hagerman, who agreed to invest heavily in the new company.

In 1890, the Mollie Gibson Mining & Milling Company was organized with Gillespie as manager and Hagerman as president.

Hagerman was approached by the owners of the Buena Vista mine, who were convinced that properties adjacent to their claim also contained gold.

Following the pattern established in Aspen, Hagerman and his partners purchased 22 adjoining properties and formed the Isabella Gold Mining Company.

The mine owners, who employed about a third of the miners in the area, extended the work-day to 10 hours while refusing to increase pay.

Although some smaller mining companies capitulated immediately, the remaining owners (including Hagerman) raised a paramilitary force under the legal protection of the local sheriff.

In 1898, Hagerman sold his stake in the Isabella Gold Mining Company and turned his remaining Colorado interests over to his son, Percy.

He built extensively on the ranch, and founded the nearby town of Hagerman to accommodate his family's needs and his financial interests.

Hagerman quickly decided to build rail and irrigation concerns in the region to enlarge his holdings.

In 1895 Hagerman donated the flat land atop North Hill in Roswell to New Mexico Military Institute, allowing the school to reopen in Fall 1898.

Hagerman wanted his line to connect with the Texas and Pacific Railway to improve local access to markets.

The line reached Roswell and Portales in 1894, and connected to the Panhandle and Santa Fe Railroad at Texico.

The Avalon Dam's rockfill structure with impervious earthfill facing was the first of its type to be used for irrigation in the United States.

The canal crossed over the Pecos three miles (5 km) south of the dam by a massive 475-foot (145 m) long, 25-foot (7.6 m) wide wooden flume built in 1890.

Despite the economic depression which had hit the nation, Hagerman poured money into reconstruction and repair of the structures, completing the dams in 1894.

Along with John Chisum, Charles Eddy and Robert Tansill, Hagerman deeply influenced development of the Carlsbad area.

He founded and built up towns and cities, donated large plots of land for public and educational use, and in general is considered one of the 'founders' of modern New Mexico.