The hike out to the creek, and the falls above, begins at a gravel-filled parking area marked with a small, easy-to-miss sign on the west end of the Castle Creek road, shortly before it crosses the North Fork on a large bridge and begins climbing up to Whalan Summit. If you park close to the trees near the paved road you might have some shade on your vehicle in the afternoon.
The trail doesn't waste any time gaining elevation, and shortly you enter the Castle Crags Wilderness. After about ¾ mile of fairly steep hiking you gain almost 500' and join the Pacific Crest Trail. This trail is called the "Dog Trail" for a very good reason — it's outside of the Park boundary so hikers are allowed to bring dogs with them. This might work to your advantage if you're a "dog person", because you can share the memories of seeing every passing dog do the "sniff the butt" routine with your dog. As fascinating as this may be to some, I usually try to get up to the PCT as quickly as I can in order to enjoy the immediate lack of gradient and more shade. The nearest source of water is at Popcorn Spring, another mile to the left after the junction and 200' higher, so bring along a good supply unless you have a filter. Almost a mile past the spring along a shady, level trail is Burstarse Creek, another source of water with pools for bathing and several impressive waterfalls upstream. At this point your round trip mileage will be close to 6 miles, so leave plenty of time if you decide to scramble up the creek to see the taller waterfalls.
The leaves of this plant [at left] do not make an acceptable substitute for toilet paper in an emergency! Learning how to identify Poison Oak will end up exhibiting infinitely more importance than, say, the order of Atomic Elements, or anything else that you may or may not have learned in high school. In the Spring the plant can be almost emerald green, making it easy to spot against a brown trail, but if it's surrounded by lots of other "emerald green" plants it's not so easy to pick out. If you really want a challenge, try spotting it during the Winter when there are no "leaves of three" to help you. This particular elevation belt seems well suited to all kinds of oaks, so do your brush-busting with care. On the plus side, in all of the cross-country "shortcuts" I've taken around here, I've never encountered any ticks or scorpions.
Rattlesnakes, however, seem to be out in force this Summer . On two different hikes a few days apart I've almost stepped on them twice. Both times, behind Castle Dome and on the PCT near Sulphur Creek, I was looking up at the scenery and not down at the trail. The Mojave Green variety I've seen north of the Crags are really "green" and stand out from the brownish dirt along the trail, but the ones in the Park were brown, quiet, and slow-moving, and looked just like a branch laying on the ground. Their rattles (almost a dozen on the snake pictured above) were vibrating as they crawled but I couldn't hear any sound.