The CBP is authorized to do citizen checks within 100 miles of the US border. The ACLU shows this on a map, here.
Now, Lake Michigan counts as a national border, probably because of the Boundary Waters Treaty of 1909, which allows Britain (Canada) unlimited navigation of all five Great Lakes.
But look at the mid-west coast. What makes the 100-mile limit lurch inland, nearly touching Reno, Nevada? Is there a national border that runs up the Sacramento River delta, perhaps to Sacramento or Stockton?
And if Sacramento, why doesn't it run up the Mississippi River?