There is actually a spring that flows periodically in the McDowell Mountains.
Nearby, ancient petroglyphs are carved into the rocks.
This is a good hike to do in late Winter or Spring, after we've had some rain. It's also good to do during monsoon season (mid-July to the end of September), after it rains. Don't go out there during a monsoon storm- you'll have lightning, dust storms, flash floods and other unpleasantness to deal with.
If you have the U.S. Geological Survey map McDowell Peak (AZ), you'll see the spring listed on there as "Mountain Spring", just north of McDowell Peak. A good website on which to view the USGS maps is TopoZone.
The spring used to supply water to Brown's Ranch. A concrete water trough, with what looks like "EO Brown, 7-14-1923" carved into it, can still be seen near the spring. On the way up, you'll see the rusted remains of the metal pipes that brought water down from the mountain to thirsty cattle and people. You'll also see newer, plastic pipes that carry the water down now. I'm not sure where that water is going, or who is using it- the golf course, perhaps? There is even a spigot where you can turn the water on and off- just watch out for the bees that are attracted to the water that drips into a puddle under the spigot.
The spring itself is not much to look at. There's a hole in the side of the hill, half-filled with stone rubble. There are iron rods sticking out of the ground. However, there is not a drop of water in sight. Below the spring opening, a metal water pipe sticks out, and the spring water travels down the mountain from there.
On the way up, you'll pass the remains of some kind of rock shelter. It will be on the right side of the trail. Take a breather and look at the names and dates carved into the rocks there.
Above the spring is a cleared-off spot on the hillside, and there is a great view back to the west, looking back over Scottsdale. Sit in the shade of the large mesquite tree there, lean back against its thick trunk, and rest before hiking back down again. Or, if you prefer, there is a faint, little-used trail that continues up the mountain behind the spring, all the way to Windgate Pass. You'll have to do a bit of bushwhacking, though.
The petroglyphs can be found alongside the trail, below the spring. I actually walked right past them on the way up. There are small, orange flags marking the petroglyphs all over the rock outcropping. Be careful not to step on them, or touch them, or disturb them in any way.
Across the gully, high on a steep hillside, are what I consider to be the best petroglyphs I've seen in the area. There are a number of representations of what appear to be antelopes, or ibexes, or some similar mammal. You'll have to climb and scramble up the steep hillside to see these petroglyphs, so be careful and use some common sense.
If you're quiet and sneaky on the trail, you may even spy a javelina getting a drink of water from the puddles that form around the hose that carries the water back down to the foothills. When I hiked this trail, I came around a corner and looked up, only to see the tail end of a javelina darting into the brush. I had startled it and interruped its drink! Unfortunately, it was too quick for me to get a picture.
From the Loop 101 Freeway in north Scottsdale: Exit at Pima Road and head north. At Thompson Peak Parkway, turn right. Continue on Thompson Peak; it will curve to the south. On the southwest corner of Thompson Peak Parkway and Windgate Pass Drive, you'll see the DC Ranch Community Center. Park there. There is a sidewalk next to Thompson Peak, and it runs parallel to that road. When you're in the parking lot, facing Thompson Peak Parkway, go to the right (south) and follow the sidewalk downhill. You will see a tunnel under Thompson Peak, where the sidewalk passes under the road. Go through the tunnel. You'll come out on the other side, in a vacant stretch of desert with houses on either side. The sidewalk will end here at a dirt trail. Take this trail between the houses and through a wash.
For more pictures of the Mountain Spring and Petroglyphs, click here.