Horses' hooves, storm runoff and natural erosion have cut trenches up to 2 feet deep in some trails at Saguaro National Park East.
Park officials are working to repair and reroute the most severely rutted trails, and some trail segments have been closed to equestrian use.
"We see ruts 24 inches deep in some places," said Shelley Lane, trail crew supervisor for the park. "It's primarily a function of the grade. The worst are trails that have taken a straight line up a steep grade."
One example is the Carrillo Trail, which departs from the popular Douglas Spring Trail, near the end of East Speedway in the northwestern part of the park.
"That trail makes me crazy; it's in such bad shape," Lane said. "But it's an example of a trail that goes straight up and down the fall line. It was there when the area was ranch land" before Saguaro became a national monument in 1933. It received national park status in 1994.
The Carrillo Trail and several others that predate the park "were not necessarily designed for sustainability," Lane said. "What we've tried to do, as time and money permits, is to reroute a badly eroded trail to where it follows contours of the land and doesn't exceed grades of 8 percent.
"It's very challenging because there aren't a lot of native materials to construct erosion-control devices," she said. The desert terrain of Saguaro Park "is not like parks with trees or places with lots of rocks."
Meanwhile, Lane said, some trail segments have been closed to livestock to prevent damage from hooves. They include the Converse Trail, the Little Wildhorse Tank Trail and a short section of the Bridal Wreath Falls Trail.
Most other trails will remain open to equestrians. Horseback riding "is a historical use of this park," Lane said. "We don't want to alienate equestrian users."
A COMPLEX PROBLEM
Lane and others emphasized that factors besides horses' hooves contribute to trail trenching.
"It's not entirely the equestrian community that's causing all the erosion," Lane said. "Sometimes it's erosion from monsoon rains" flowing down steep and poorly designed trails.
Mark Flint - an expert trail designer who is a hiker, mountain biker and horseback rider - said blaming equestrians for the problems "fails to address root causes."
"The problem with the trails in Saguaro is not the type of use, but a combination of design and volume of use," said Flint, known for his work on the Arizona Trail near Tucson. "I don't care what type of use you put on a trail - if water is allowed to run down it, you are going to have erosion. Volume speeds up the process, and Saguaro is a heavily used park, especially the lower trails."
Flint emphasized that "the solution is sustainable trail design. In the places where they have rerouted to a sustainable design, you can see a much more stable tread."
A sign board at the Broadway Trailhead in Saguaro National Park East includes this notice: "It is easier for a hiker or runner to move out of a trenched trail than it is for a horse rider. Please be courteous."
Contact reporter Doug Kreutz at email@example.com or at 573-4192. On Twitter: @DouglasKreutz