The Cowboy Trail Rides Trailhead is located in Red Rock Canyon National Conservation Area, but outside the Scenic Loop area. The trailhead is about 30 minutes west of Las Vegas.
From town, drive out to Red Rocks.
From West Charleston Blvd at Highway I-215, the "Western Beltway" (Table 1, Site 516), drive west on Charleston Blvd (Highway 159) out into the desert. Pass the turnoff into the Scenic Loop Area (Site 519), and continue west on Charleston Blvd. for 1.1 miles to the "Horseback Rides" parking lot on the left (southeast) side of the road (Site 853). Park here; this is the trailhead.
From the other direction, the trailhead is 1.2 miles north of the Scenic Loop Road exit (Site 532).
Link to trailhead map.