So motoring down a ridge is infraction if hikers are there ?????


That is correct. read FAR 91.119 (c):

"Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

Like I said, everyone who has ever been down a ridge with a "structure" or a "person" on it has violated this section. Most don't get caught . . . Some do.

ROY