California had a per capita income of $29,906 during the five-year period comprising years 2010 through 2014. About every third county and every third place in California had per capita incomes above the state average. Though somewhat counterintuitive, this implies that counties and places with per capita incomes even slightly exceeding that of the state can be classified as "high income" given the natural division of places into a top third (high), middle third (medium), and lower third (low) when ranked by per capita income. Hence, the upper third of all places in this ranking have a per capita income with a lower bound roughly equal to that of the state, about $30,000. The median place and county in California had a per capita income of roughly $25,000, and the lower third of both types of geographies had per capita incomes with an upper bound of about $20,000. Places and counties with the highest per capita income were concentrated in the San Francisco Bay Area, which has a relatively high cost of living. Those with the lowest per capita incomes were concentrated in the Central Valley, an economy in which agriculture assumes a primary role.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.