Poplar

Yellow poplar (Liriodendron tulipifera) is one of the most useful hardwoods in the eastern U.S.: light, stable, easy to machine, and smooth under paint. It's the standard choice for painted trim, casing, and crown molding. That white horse fence is very likely poplar. Boards carry natural mineral streaking in green, gray, or occasionally purple, part of the wood's character at scale. An interior wood by default, domestically sourced for trim, millwork, and paneling.