Oregon Revised Statutes Animals § 608.350

No railroad track shall be deemed to be fenced within the meaning of ORS 608.340 unless it is guarded by such fence against the entrance thereon of any livestock on either side of the track, and not more than 100 feet from the track. Whatever is a lawful fence in the county where the killing or injury occurs, and no other, shall be deemed a lawful fence under ORS 608.340. However, complete natural defenses against the entrance of stock upon the track, such as natural walls or deep ditches, shall be deemed to be a fence under such section, when it, in connection with other and ordinary lawful fences, forms a continuous guard and defense against the entrance of such livestock upon the track.