The top of Palomar Mountain is home to the Palomar Observatory. Three large telescopes, the 200-inch Hale telescope (which can be seen from many distant mountain tops), a 60-inch telescope, and the 48-inch Samuel Oschin telescope are currently used for ongoing research. The Observatory has been in operation since the mid 1930’s, and has been involved in numerous discoveries, including the discoveries of dwarf planets Sedna and Eris, 178 supernovae, and 13 comets.
If you want to visit the Observatory you can drive there, or you can park down the road at the Observatory Campground and hike this 2 mile trail through some beautiful oak and pine forest. As you can probably guess, we took the trail.
Driving in to the campground, we found a large map at the entrance that helped us locate the trailhead. There was also a self-pay station here where you can pay the $5 day use fee if you don’t already have an Adventure Pass.
Following the map’s guidance, we drove around the campground to find the Observatory trailhead and parking just opposite campsites 19 and 20. There were only a handful of parking spots here, so if you’re organizing a group hike make sure you plan for carpooling.
The trailhead wasn’t terribly well-marked, but we spotted an old, worn trail marker and blank information board just beyond a wooden fence and interpretive sign for the Laguna mountains skipper butterfly, and we set off up the trail.
The trail curved to the right, passing behind the campground’s amphitheater, and began to climb upward. 
As we were hoping, the trail had significant tree cover and was well shaded. Towering oaks created a thick overhead canopy, and the ground was covered with brown, fallen leaves.
At .36 miles we passed a small spring on the side of the trail, which was producing just enough water to moisten the ground.
The trail undulated up and down hill (mostly up), but wasn’t especially difficult. 
Around the half mile point we came upon a wooden deck on the side of the trail.
Here we had a beautiful view of the Mendenhall Valley below.
At .64 miles we crossed a small wooden footbridge that spanned a narrow ravine.
Another tenth of a mile brought us to the top of an oak covered rise. A wooden bench provided a comfortable spot to rest and enjoy the peaceful tranquility of the woods.
On the other side, the path continued through the cool, dark oaks. At the bottom of the slope a dry creek was full of tangled green brush.
As we continued, we began to note more and more poison oak along the sides of the trail. A few stray branches protruded into the middle of the trail. It was easy enough to avoid so long as you paid attention.
Continuing on, the trail wound its way uphill. We heard the distinctive knocking of a woodpecker, and looking up at a dead tree to the side of the trail caught sight of an acorn woodpecker.
We knew we must be getting at least somewhat close to the Observatory when we spotted a promint “Private Property” sign warning us to stay on the trail, indicating the boundary between National Forest land and the California Institute of Technology property.
Around 1.1 miles we came to the top of a rise and found another bench. On the opposite side of the trail was a huge patch of almost leafless poison oak. quietly waiting for unsuspecting hikers.
We continued on through more beautiful Coulter pines and various oak trees. We caught a few glimpses of the road through the trees, and the occasional roar of a motorcycle out for an early morning ride broke the silence.
Another quarter mile or so brought us to another darkened oak grove. 
Around 1.6 miles we passed yet another peaceful bench near an idyllic copse of oak trees. This trail was packing a huge amount of serenity into such a short hike.
We emerged from the cover of the oaks and had a short stretch of exposed trail before finding some more trees.
We spotted an enormous clump of Poodle Dog Bush on the right side of the trail, and some smaller specimen to the left. If you’re not familiar with Poodle Dog Bush, it is a severe irritant that causes rashes and itching more extreme than poison oak. When in bloom, it has beautiful tubular purple flowers that can be breathtaking to view, but don’t touch this stuff!
Fortunately, despite the size of some of the bushes alongside the trail, it was all well off to the side and it was easy to pass unscathed.
Shortly beyond, we came to the end of the trail, with its aged but charming trailhead sign.
We were right next to the road that led a couple of hundred feet up to the Observatory parking lot. Unfortunately, while our early start was beneficial for avoiding the heat, it meant we arrived before the Observatory opened at 9am. 
We contemplated hanging around for a while until it opened, but the weather was already warming up a bit, and we still had another trail we wanted to hike after this one. So we decided we’d head back, get all our hiking done, and then just drive back up to the Observatory later. So that’s what we did.
The Observatory Grounds are open from 9am to 4pm during Daylight Savings Time, and from 9am to 3pm during Standard Time. There’s no admission fee so this is a fun little adventure to add on to your hike. There’s a nice little picnic area right off the parking lot with tables and more of those impressive oak trees to enjoy.
Heading up the path there is a Visitor’s Center with a small museum and gift shop to explore. You can also buy tickets for a slightly more comprehensive tour than you’ll get just by walking around in the gift shop.
Continuing up the path you’ll see the enormous white dome of the 200-inch Hale Telescope to the right. You can go into this building and up a flight of stairs to view some informational exhibits and view the telescope through a glass window. If you take the tour you get to actually go inside the dome floor.
Check out the Observatory’s web site if you want more information about visiting the facility.
View the full photo gallery
Directions:
Take I-15 north to the Via Rancho Parkway exit. Turn right onto E Via Rancho Parkway, continue as it turns into Bear Valley Parkway. Turn right onto E Valley Parkway, continue as it turns into Valley Center Road. Turn right onto CA-76 East. After approximately 6 miles, make a slight left onto S Grade Rd/Palomar Mountain Rd. Continue up the mountain for 6.7 miles, then turn left to stay on S Grade Road. Continue on S Grade Road for approximately 2.4 miles to the Observatory Campground on your right. The trailhead and parking are about halfway around the campground loop, across from sites 19 and 20. map
| Total Distance: | 4 miles |
| Difficulty: | Moderate |
| Total Ascent: | 891 feet |
| Dog Friendly?: | Leashed dogs allowed |
| Bike Friendly?: | Bikes allowed |
| Facilities: | Pit toilets and water at campground; flush toilets and water at Observatory |
| Fees/Permits: | Adventure Pass required at campground, or park at the Observatory for free and do this hike in reverse |
For more information, visit:
Cleveland National Forest – Observatory Trail
View route or download GPX in CalTopo
