Tucson area
I just asked this question , about Tanque Verde Falls trail, to someone who lives in Tucson and has taken this hike recently. It's still a clothing optional trail but like in many circumstances, you'll find more clothed people on the trail than you do nudes. Apparently, there are two trails, with one being the clothing optional trail, and all the clothed people take the clothing optional trail... I wonder why (stating so sarcastically).
We may visit this area some day soon. If we do and we take this hike, I will report back in a couple weeks. It's possible that member who lives nearby and in Tucson, will respond with more accurate info.
The upper Tanque Verde Falls trail is indeed clothing optional. Depending on the day and the time of your visit, the number of clothed hikers you see can range from 0 on up. Weekends are of course busier for visitors of all persuasions. To find the trail, visit this TN page or look on Google Maps for Tanque Verde Falls Beach.
A word of caution: If you look on Google Maps, do NOT take the trail marked "Upper Tanque Verde Falls Trailhead" at 32.25738, -110.65593. This trail is textile, rather steep and will take you *below* the upper falls, downstream of the clothing optional area. The trail you want is 100 yards (90 meters) further up Redington Road at 32.258, -110.6555. It heads due east, will take you right to a nice beach above the upper falls, and is clothing optional as soon as you are out of sight of the road.