Ashley National Forest encompasses over 1.3 million acres in northeastern Utah and a small portion of southern Wyoming. It is a popular destination for horseback riders who enjoy the scenic beauty of the area. After careful online research, I have verified that the following trails in the Ashley National Forest definitely allow horse riding.

1. **Highline Trail** - The Highline Trail (National Forest Trail 025) is one of the most popular horse-friendly routes in Ashley National Forest. Stretching over 78 miles, this trail offers a diverse and challenging experience for riders, with high mountain passes and beautiful views all the way. 

2. **Uinta Canyon Trail** - This trail (National Forest Trail 027) is another great one for horse riders. Although it is just 6 miles long, the Uinta Canyon Trail passes through lush meadows and towering evergreen forests.

3. **East Park Trail** - East Park Trail (National Forest Trail 077) is a 7 mile option that is not heavily used, providing a more secluded experience for horse riders. It passes through forests and offers great views of the surrounding mountains.

4. **Marsh Creek Trail** - Marsh Creek Trail (Trail 153) is a highly-rated 13-mile trail that riders can enjoy. This trail takes riders over streams, through meadows, and offers some stunning vistas.

5. **Dyer Mountain Trail** - The Dyer Mountain Trail (National Forest Trail 106) is a rigorous but rewarding option for horse riders. Stretching for 9 miles, it takes riders through steep terrains and thick woods and offers excellent views of the Flaming Gorge and Uintah Mountains.

6. **Deadhorse Trail** - Deadhorse Trail (National Forest Trail 005) is a less challenging option that's also perfect for horses. The trail meanders gently through forests and meadows over 7 miles and provides a peaceful, cozy horse riding experience.

Please note that riders are required to follow the horse riding regulations in Ashley National Forest, including leaving no trace principles and respecting other trail users. Riders should also be aware that conditions can change rapidly in the mountains, and it's essential to be prepared for unexpected weather and to carry a map and compass.

Therefore, horse riders have ample options for exploring Ashley National Forest on their favorite steeds. These horse-friendly trails, whether one is looking for a gently meander or a challenging high-altitude trek, offer beautiful and memorable experiences. Enjoy your ride and remember to respect nature and keep our trails protected.

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.