Only open on Irvine Ranch Natural Landmark's Wilderness Access Days. It may or may not be open for use on these days. More information can be foud at the Irvine Ranch website
Shoestring is part doubletrack, part singletrack and part paved road near the trailhead. The singletrack portion runs parallel to Santiago Canyon Road. There are a couple of tough parts because of the grade, but it's not overly technical or rocky. There's a short curved bridge across a creek which is unusual. The singletrack takes a hard right angle turn into a doubletrack that is much more nuanced in difficulty but will still take some work due to the elevation gain.
There are some incredible views of the Santa Ana and San Gabriel Mountains once you gain some elevation on the doubletrack section. The doubletrack is dark soil/dirt vs. the singletrack which is the typical SoCal dusty type trail.