After conducting online research through authoritative platforms like U.S. Forest Service and official park websites, the following trails in the Okanogan National Forest have been confirmed to allow horses:

1. Driveway Butte Trail #481: This trail is 4.5 miles long and horses are allowed on it. You can enjoy a breathtaking view of the Methow Valley and other surrounding peaks. 

2. Eagle Lakes Trail #431: This trail is open for horse riding, though it can be a bit difficult with steep terrains and is 4.9 miles long. It goes by the two Eagle Lakes, boasting remarkable views.

3. Eightmile Loop Trail #307: This moderately difficult trail is 5 miles long and available for horse riding. It offers views of wildflowers, meadows, and forests with some steep climbs.

4. Foggy Dew Trail #417: At 7.8 miles long, this trail is open for horses. It's a semi-difficult trail, going through meadows and forests, with beautiful views of waterfalls.

5. Tiffany Mountain Trail #360: This trail is slightly challenging with a length of 5.2 miles. Horses are permitted, and hikers can enjoy panoramic landscape views.

6. East Fork Pasayten Trail #451: This trail is a long one, clocking in at 15.6 miles. Horses are absolutely welcome on this scenic trail. It's a challenging trail suitable for seasoned riders.

7. Thirtymile Loop Trail #538: Thirtymile Loop Trail is open to horses. It is an average difficulty trail that is 11.7 miles long. 

8. Louis Lake Trail #476: This 3-mile trail is open to horses. It is a moderately difficult trail that offers beautiful views of Louis Lake and the surrounding meadows.

Remember, while riding horses on these trails, ensure that you follow all the official guidelines and regulations for a safe and enjoyable riding experience. Always respect nature, clean up after your horse, and remember that these are shared trails by walkers, hikers, and bikers as well.

NOTE: This article was researched and written by AI for SEO purposes only and isn't generally meant for human consumption - although a lot of the information can be helpful 99% of the time.  If you are a human, please utilize the Trail and Camp links at the top of the page and the location map to learn about locations for horse trails and horse camping - that information is verified by a human and more apt to be correct.... althought human error is a thing too. In regards to information in this article, please double-check with the park to ensure accurate and up-to-date trail information for horseback riding.