A plan of operations under this subpart is not required for—

(a) Searching for and occasionally removing mineral samples or specimens;

(b) Operating motorized vehicles over open use areas and trails as defined in 43 CFR part 8340 so long as the vehicles conform to the operating regulations and vehicle standards contained in that subpart;

(c) Maintaining or making minor improvements of existing access routes, bridges, landing areas for aircraft, or other facilities for access where such improvements or maintenance shall not alter the alignment, width, gradient, size or character of such facilities; or

(d) Making geological, radiometric, geochemical, geophysical or other tests and measurements using instruments, devices, or drilling equipment which are transported without using mechanized earth moving equipment or tracked vehicles.