The only way to reach the Hozomeen Campground in the Ross Lake National Recreation Area (Washington) by vehicle is from Canada, but there is no corresponding Port of Entry on the CBP list. This is curious. Both the NPS and this article from a Seattle-based magazine mention its remoteness, but don't mention border formalities, except for:
the border’s presence was recorded almost entirely by absence: no people, no walls, no gates, only a small sign, a tiny monument, and a mind-blowing work of art.
Canadian and American campers, boaters, kayakers, and hikers mingle freely across the open border. (Albeit carrying ID: “Just be prepared,” Kinsey Shilling warned. “Border Patrol is in the area and they do check people.”)
And the NPS just states:
Located 40 miles (64 km) south of Hope, B.C. on Silver/Skagit Rd. To reach Hozomeen take the Silver/Skagit Road from Highway #1, Exit 168, 2 mi (3 km) west of Hope, B.C. Travel south for 40 miles (64km) to reach the campground, Ranger Station, and boat launch. The Silver/Skagit Road is maintained but unpaved and often rough, carry a spare tire. For current road conditions refer to the road conditions report. Hozomeen Campground is not accessible by road from the U.S.
What are the formal requirements for crossing the US/Canada border at Hozomeen? Is it limited to citizens of US and Canada? Are there CBP officers to check and stamp passports? Or is this done by NPS staff? Is there a special permit?
What I was expecting is something similar to the Boquillas del Carmen border crossing information at Big Bend National Park, or information such as about the Pacific Crest Trail Canada entry permit around 20 km east of Hozomeen. The Pacific Crest Trail Association (PCTA) also notes that Entering the US from Canada at the Pacific Crest Trail is illegal because there is no official port of entry. Surprisingly I can't find any formal border crossing information for the Hozomeen border crossing.
Edit: According to the Center for Land Use Interpretation, There is no Port of Entry to report to here. People who cross south of the boundary have to drive back through Canada, so they are not expected to report to US officials, even though they might have camped on US soil, for days or weeks. I don't know how official this information is, considering that the same page describes entering the USA on a nearby hiking trail as Hikers crossing the line are technically supposed to report to the nearest Port of Entry, but many do not., when other sources states this is illegal. On the other hand, Wikipedia claims that the Hyder-Steward border crossing is the only land border crossing where a person may legally enter the United States without reporting for inspection, implying entering at Hozomeen requires inspection (perhaps by NPS rangers?) or is illegal, but Wikipedia might be wrong here.