Canyons are inherently risky. Flash floods occur without notice on sunny days. Technical skills & surrounding topography knowledge required yet does not eliminate risk.
Paved Road Peak Bagging!
Mule Peak is the highest point along this area of the frontal range, and is more typically visited by simply riding your ATV up FR 90A from West Side road. This route uses the more difficult, and much more fun approach from the valley up Mule Canyon drainage, traversing on to Burleson Ridge, connecting with an old Jeep track on top of the ridge then enjoying a nice upper meadow shortcut connection to the old paved road to the peak.
The peak houses the ruined remains of an old Observatory complex... with the run down and abandoned buildings of the living quarters, work spaces, and the interesting telescope building, complete with sliding track roof. The telescope left in the building strongly resembles the unit from the movie "Alien"... wherein there is a seat for one person that straddles the large telescope. Sort of an eerie site.
The paved road accessed this complex from FR 90A, and also looped out to the far end of the ridge line. It is that portion that is reached from the meadowed traverse. You may skip the meadow cut and simply continue to wind your way around the south and east side of the mountain; it all leads up to the top.
This hike begins following the Mule Canyon drainage, initially a very easy hike with great towering Buttes and ridges and interesting rock strata. After the first few miles, the hike begins to pose ever greater challenges as you get closer and closer to the large waterfall blockage around 3.6 miles in. At the waterfall you will have the option to traverse up and around on either side with a very steep scramble... or, if you're skilled enough, the falls are probably climbable.
Once past the falls enjoy a very nice section of more intimate canyon, finishing up with a grotto like enclosure and a final easy climb out. Once above this point you hike for a short distance into a very open basin. You want to begin looking to your right... your goal is to exit the canyon bottom and make your way up to the ridge line to the south.
Do not wait too long to make your exit. If you reach the slab bottomed section of the canyon with the steep walls on the left (complete with a bit of cactus hanging gardens) then you've gone too far. There are some small falls (3-5 feet) that make for an ideal place to exit the bottom and move back to your right... winding both south and west toward the ridge. Paths through the hillside scrub oak open up nicely. You'll soon find yourself on the ridge and connecting with the old double track. Follow it to your left towards the obvious high point ridge.
As you make your way around the south side of the mountain, you have the option to follow the road the entire way, or take the more pleasant up meadow shortcut to the top. Look for the obvious drainage cut and meadow as you work your way below the ridge cliffs, and turn to your left enjoying this tree covered route. Enjoy the surprise of cresting out on to a paved road! Turn right and follow the road up to the old observatory.
Return by the same route... you do not want to make the mistake of dropping down into the upper portions of Mule Canyon. It is nasty overgrown with briars... not a good thing. Enjoy the open course of the roadway and easy traverse back down into the canyon just above the grotto.
You may want to consider bringing along a rope to rappel down the waterfall. It will save you a nasty scramble descent (it is really worse going down than it was to go up).
Give yourself an early start for this longer, more challenging day. Or, arrange a shuttle out on FR90/FR90A. You could have a car awaiting you at the Observatory if you wanted to!
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.