Karlo is an unincorporated community

Unincorporated area

In law, an unincorporated area is a region of land that is not a part of any municipality.To "incorporate" in this context means to form a municipal corporation, a city, town, or village with its own government. An unincorporated community is usually not subject to or taxed by a municipal government...

 in Lassen County

Lassen County, California

Lassen County is a county located in the northeastern portion of the U.S. state of California. As of the 2010 census, the population was 34,895, up from 33,828 at the 2000 census...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It is located on the Southern Pacific Railroad

Southern Pacific Railroad

The Southern Pacific Transportation Company , earlier Southern Pacific Railroad and Southern Pacific Company, and usually simply called the Southern Pacific or Espee, was an American railroad....

 in the Secret Valley 20 miles (32 km) east-northeast of Susanville

Susanville, California

Susanville is the county seat of Lassen County, California, United States. Susanville is located on the Susan River in the south-central part of the county, at an elevation of 4186 feet . The population was 17,974 at the 2010 census, up from 13,541 at the 2000 census...

, at an elevation of 4432 feet (1351 m).

The Secret post office opened in 1892, closed in 1895, reopened in 1896, changed its name to Karlo in 1911, and closed for good in 1934. The name Karlo honors Frank De Carlow, who settled nearby in 1886.