Easy, some route finding needed
Mount Trumbull is on the north rim of the Grand Canyon. If you've ever walked along the south rim, perhaps you've seen a sign pointing to Mount Trumbull, 80 miles away. If only it were that close . . .
If you've only seen the south rim, do yourself a favor, carve out a few days, and head north. You can either go by way of Las Vegas and St. George, Utah on the west, or Jacob Lake and Fredonia on the east. An invaluable resource is the Arizona Strip BLM map (if only the Phoenix BLM office had one!), which offers so many possibilities, you'll never want to leave. Mount Trumbull is about 50 miles and 3 hours down bumpy dirt roads from either St. George or Fredonia. You will pass a ranger station/house, but there are no collection facilities for the entry fee. Save the money for a wheel alignment when you get home. If you're in St. George, stop at the Arizona Strip BLM office. Sorry to spend so much time on getting there, but it does take planning, a good map, and a LOT of driving. You will not see many people, if any, so be prepared for vehicle problems. Your cell phone WILL NOT WORK out here, even on top of Mt. Trumbull!
OK - the hike. The road to the trail is well-signed, and there is a BLM site right next to the trailhead. Get your water here, there's none on the trail. Trail starts out easy enough, climbing through huge old ponderosa pine. Trail is easy to follow, until . . . probably 2/3 of the way up, the trail ENDS! They did that on purpose, so if you're hazy on route-finding, stop here and go back. Otherwise, keep walking/scrambling up.
Mount Trumbull, like most of the mountains in northern Arizona, is an old volcano. Sunset Crater near Flagstaff is the epitome and best example. I said "scramble up", because where the trail ends, cinders several inches deep cover the mountain the rest of the way up. You can follow footprints up, and hope the person before you knew where he was going. But generally, if you keep going up in a zig-zag (much as a skier would go uphill), you'll be OK. One thing you will want to do at various points on the hike, is get a compass reading on where your vehicle is parked. That way, on the way down, you'll know where you need to end up, and eventually you'll hit the trail.
As for the summit, there is a marker and a register. So I've read, because I couldn't find it. There is described a "false summit" where you think you're at the top and can't go any higher. That's where I ended up. After having some trail mix and wandering around, I went back down. I went in July, and it was pleasantly cool. The views are terrific, when not obscured by the pines.
After the hike, do yourself a favor and drive to Toroweap, on the north rim. There are plenty of places to camp, and there might actually be a few people there. It is one of the most gorgeous overlooks on the Grand Canyon. It's also one of the most scary - there are no rails, it's very windy and a lo-o-ong way down. You won't see God, but you'll know He was there. Check this map for directions. Please note, it is in the National Park so a backcountry permit is required to camp. You might be able to snag a last minute permit at the North Rim Backcountry Office, call ahead to be sure.
Check out the Official Route and Triplogs.
BLM Division Reports The Mt. Trumbull trail quickly ascends the south slope of this high basalt-capped mesa. From the southern rim of the basalt cap, the trail ends and the final mile to the summit on the north edge of the mesa is trailless. Once atop the mesa the route to the summit passes through a beautiful forest of ponderosa pine. At the northern edge of the mesa, broad sweeping views of the heart of the Arizona Strip, as well as much of southern Utah, await the persistent hiker.
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.