The CBP is authorized to do citizen checks within 100 miles of the US border. The ACLU shows this on a map, here.

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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?


The immediate explanation is the substantial eastward jog created by Suisun and Grizzly Bay. This would follow from 33 CFR 2.20, defining the territorial sea baseline, following the Convention on the Territorial Sea and the Contiguous Zone. The zone would fall just short of Lake Tahoe. It's based on tidal waters, see 33 CFR 329.12 for similar definition of the US baseline in terms of waterbodies subject to tidal action.

  • And this is even shown on the map in the question, the enormous three grey spots that protrude into the area being queried. – Nij Jul 28 at 7:49
  • @Nij but there's also one of those near Portland. No bulge. – Harper Jul 28 at 13:13
  • Hence the explanation of why one does, not the other, in the answer. – Nij Jul 28 at 19:19
  • I believe that the entire San Francisco Bay would be internal waters, landward of the baseline. – user102008 Aug 1 at 18:20

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