Millions of low-income Californians eligible for food stamps are not receiving the benefit, earning the state one of the lowest rankings in the nation for its participation in the program.

Just three states — all much more conservative than the Golden State — have lower rates of participation, according to the latest available data from the U.S. Department of Agriculture.

About 4.1 million Californians, or 70 percent of those eligible, are enrolled in the food assistance program, called CalFresh. That leaves about 2 million who could be getting the benefit but aren’t, according to a January report citing the 2015 federal data.

The national average is 83 percent. Several states — including Illinois, New Mexico and Oregon — report 100 percent enrollment of those who qualify for the food stamp program, known at the federal level as the Supplemental Nutrition Assistance Program, or SNAP.

California officials say they’re puzzled by the low rate of participation. But they suggest it may be due to the less-than-optimal quality of customer service and a bulky bureaucracy, including long lines at county offices and lack of flexibility in setting appointment times.

For more, read Anna Gorman and Harriet Rowan’s “‘A Persistent Puzzle’: Californians Embrace Medicaid — But Food Stamps? Not So Much.”