Aircraft N4227E
The Bell helicopter may be on a regular route such as pipeline patrol or other commercial venture as it is registered as corporate owned. It is certified with extended range fuel. The horses may be scared up incidental to the helicopter's regular mission. Also, what is TOO low over the river area in your observation? Estimate the flight altitude in feet.
You may wish to inquire at the nearest FAA General Aviation District Office with your complaint-be specific on N number, place, date and times of observation.
TOO low is below 500 feet, which is what this aircraft was flying. We have photos to substantiate this report if need be.
Again, contact the local FAA re your concern. You may also consult the Federal Air Regulations Aeronautical Information Manual. My recent one is over 1,000 pages. Helicopters if on floats may have special rules. The Bell turboshaft helo may be on a legitimate commercial mission requiring flight below 500' AGL, such as, for example, fish stocking of the river, which can be done legally from the air. The below 500' AGL restriction has some caveats you may not be aware of. I'm done here.
This aircraft is also on the On-call USFS list. It may well be a survey flight.
US 91-119 says...
An aircraft must maintain 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.
Wild horse habitat sounds 'sparsely populated" to me....
So...which was more frightened, you or the horses? : :