This one surprised us. Having got an early start, we hiked the Bristlecone Trail and then decided to hike to Mary Jane Falls since it is only a mile and a half. Easy one! Well, not really. It's a mile and a half - almost all uphill!
The trailhead is reached by driving up Kyle Canyon Road (Hwy 157) and turning right on Echo Drive. The trailhead is about a quarter mile on the left. The trail begins going up the canyon with a gradual rise in elevation. This soon changes as you enter a series of steep switchbacks. You don't get the reward of looking back and seeing how much elevation you have accomplished since the trees are so close. Just when you are sure you've reached the top, you are "rewarded" with a long series of steep rock steps that lead to the falls.
The falls were still dropping in two areas on this July day. We could imagine how great the falls must have been during the prime snowmelt in late May. The area we stood in was probably a deep pool of very cold water. On our return down the switchbacks, we encountered a couple groups with children. Though I would not recommend this hike for kids under 5, those we passed seemed to be doing well with the trail. Maybe we found it hard since it was our second trail of the day.
Following are pictures with some comments.

The trail is well defined and all uphill.

The steep steps run for about an eighth mile.
The falls have slowed to a trickle in July.
The canyon remains cool despite 100 degree temps in Las Vegas..