Josh Grant describes the route (2WD access version, 50+km as described):
This is Death Valley's premier big loop route with so many reasons why:
1) It's a loop, no car shuttle issues. Titus Canyon is a GREAT run, super scenic, but the car shuttle can be onerous and there's no water until about the end.
2) The loop is beautiful and varied. You start off in a broad wash, with occasional glimpses of the beautiful narrows that are the highlight of the day coming near the end of the day. You go through riparian springs, Cottonwood actually flows well enough to dunk your head into for cooling. The high point of the course is at about 4,900 feet and populated by high desert scrub and sage, then you drop into Dead horse and marvelous Marble canyon after that.
3) Cottonwood Springs flows year round and you pass through it at about 14-15 miles in. The second major spring, Dead horse spring may be more ephemeral and definitely doesn't put out as much water but if it is flowing is perfectly situated at about the 21 mile mark.
4) Easy logistic access 1/2 hour on an easy dirt road to Stovepipe Wells. There's a restaurant, bar, store, hotel rooms and gas available right there.
The loop itself starts at the 2wd parking area, specifically the only permanent fixture there - the no fire sign located at 36.642518° -117.270530°. This starting area gives more people the opportunity to run it without a high clearance/4wd vehicle and only adds 4.5 miles to the loop proper. Head into the canyon from the parking area and then head left along the Cottonwood canyon trail. It's pretty foolproof, follow the wash and the tire tracks (the first handful of miles are open to vehicles but you probably won't see much if any traffic up here the road is not maintained.
You'll come across an unnamed riparian area with a spring that rarely flows around mile 12, don't count on water here but you might get lucky. Keep on going to Cottonwood for a real refill and resupply point. Once you get to Cottonwood, stay left out of the brush or you'll regret it. Refill here and you're going to start heading north, up canyon. The next four miles are a slow, exposed uphill and can be sloggy because you're in a sandy wash and gaining over a thousand feet along the way. Watch out for this section, it can get baking hot even on a moderate day.
The navigational crux comes up next as you need to drop into Dead horse canyon and then into Marble canyon after that. Get yourself a good GPX file to follow, or be great at terrain association and topo map usage. The technical crux of the course is a very steep downhill section just past mile 20 and then a 10 foot dryfall to down climb about a mile later. I've found no way around this one, so if you're not comfortable with the idea of it by the time you get here you're in trouble. After this is the smooth buttery downhill section you've been waiting for. These next ten miles are about as good as it gets, enjoy the payoff.