However, under certain circumstances, payment for personal services performed in the United States is not considered income from sources within the United States. For example, personal services performed by an independent nonresident alien contractor specifically exempted by a tax treaty. For more examples, see the Pay for Personal Service section in Publication 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.
Seven of the ten counties in California with the lowest per capita incomes are located in the Central Valley. Two of the remaining three are rural counties in Northern California. This leaves Imperial County, which shares California's portion of the U.S.-Mexico border with San Diego County. All of these counties had populations not exceeding 1,000,000, and all of them are landlocked, with the exception of Del Norte County.