USGS Water Data APIs

The USGS Water Data OGC API — an OGC API Features service declaring 18 conformance classes, including OGC API Common Parts 1-3, Features Parts 1-4 and CQL2 filtering, and serving 37 collections. Verified live 2026-08-30: /conformance returns the class URIs, /collections returns 37 entries, and the landing page advertises a first-party OpenAPI 3.0.2 with 189 paths at its service-desc link. A control path on the same host returns 404, so the host discriminates and the 200s are evidence rather than a catch-all. The live /conformance endpoint is NOT registered as a property: `Conformance` is the local artifact type (5,889 providers use it for conformance/*.yml on disk), and there is no pointer class meaning a live OGC conformance endpoint. That gap is roadmap#80's failure mode 3, and overloading an existing type to work around it would hide the gap rather than record it. The classes are captured in conformance/ with their source URL.