When operating on an unpublished route or while being radar vectored, the pilot, when an approach clearance is received, shall, in addition to complying with [section]91.
You probably got blue in the face with the first part of this reg, about seeing the paint, pavement or lights, but you might not be so sweet on paragraph (i) Operations on unpublished routes and use of radar in instrument approach procedures.
The issuance of the approach clearance when the flight was 44 miles from the airport on an unpublished route
without clearly defined minimum altitudes.
When issuing cruise in conjunction with an airport clearance limit and an unpublished route
will be used, issue an appropriate crossing altitude to ensure terrain clearance until the aircraft reaches a fix, point, or route where the altitude information is available to the pilot.
65R states criteria for issuing approach clearances for aircraft operating on unpublished routes