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How a dam and tunnel tamed Globe’s wild and wooly McCormick Wash

The concrete spillway with the author's dog (for scale). Photo by Kim Stone.

Any visitor driving along the edge of downtown Globe on Highway 60 has to be struck by the steep slopes that the entire town seems to be clinging to. Not so apparent are the natural drainages—washes, gulches, and creeks—that funnel away the rains that can fall with frightening intensity, particularly during the monsoon season.

One of the most notorious of these drainages is McCormick Wash, a relatively benign-looking wash that snakes its way diagonally, from northeast to southwest, through the heart of Globe’s historic residential district and downtown. Its beginnings are further to the north, collecting rainfall that runs off the higher elevation hills and dales of the Copper Hills.

After negotiating the crisscross of residential streets, the normally dry McCormick Wash meets Sycamore St. where it abruptly turns west and follows the street down the hill. From this point on, it is artificially constrained within manmade drainage channels.

When enough rain falls for the wash to run, the water follows an open concrete channel that was built in the early part of the twentieth century along the north edge of Sycamore to between Devereux and Hill St. From here, an underground masonry and concrete channel constructed even earlier takes over. It moves water in a curious angled route from the post office under Hill St., Broad St., and the railroad tracks before it deposits its load of water at a concrete discharge point constructed on the bank of Pinal Creek.

Historic floods

This is the tunnel that carries water nearly 700 feet through a mountain from the McCormick Wash diversion dam. What looks like the light of an oncoming train is actually daylight at the outlet into the copper gulch. Photo by Kim Stone

When it comes to epic floods in Globe, Pinal Creek gets all the glory. The damage to Broad St. in 1904 and exactly 50 years later in 1954 are testimonies to its ability to overflow its banks when the need arises. But McCormick Wash doesn’t drain a huge area in the Pinal Mountains like its bigger brother does, so it only runs when heavy rains fall in a short period of time on its relatively small watershed up in the Copper Hills.

This is what happened in 1918 and again in 1923, when McCormick Wash far exceeded the manmade drainage channels’ ability to contain it. In both those years, it flooded the Holy Angels Catholic Church basement, and in the 1923 event, it damaged structures and left a few inches of muddy muck on the green grass at the Eastern Arizona train depot. The 1918 flood alone caused $200,000 in damage to downtown buildings.

These were notable McCormick Wash transgressions, but there was other flood damage, too, and the Globe City Council had been paying out for property damage claims for a number of years. They were ready and receptive for new ideas to tame the wash.

A better idea

Suggestions for flood mitigation included making Sycamore Street concave (like Adonis Ave. in Miami), but the best solution—and the coolest—came from the Globe-Miami chapter of the American Association of Engineers.

They came up with the idea to build a dam across McCormick Wash.

This dam wasn’t meant to impound a reservoir for future bass tournaments or water skiing. Instead, it would divert the water flowing down McCormick Wash into a completely different drainage. While the dam idea was pretty straight forward, directing the water to Copper Gulch, the next drainage to the west, would require tunneling 650 feet through a mountain. The idea took some daring creativity and it was received with immediate enthusiasm.

The engineering plan called for an above-ground concrete spillway to carry the water from the 20-foot-high dam about 300 feet to the entrance of the tunnel. The tunnel itself was to be 8 feet by 8 feet without any timbering or reinforcement. The dam would be 120 feet long with a 60-foot- long wing wall to guide the water into the concrete spillway.

A map by writer, Kim Stone, shows the path of the McCormick Wash.

Julius Milton, one of the engineers who designed the flood control project, estimated that the diversion into Copper Gulch would remove five-sixths (over 80%) of the water that would otherwise flow through town.   

The expected cost for the McCormick Wash Flood Control project was $18,600 and the Globe City Council gave the go-ahead to start construction in September 1923. It was completed in 1924.

The first storm of any consequence to test the finished product wasn’t until August of 1925. The amount of rain wasn’t reported, but the Arizona Silver Belt wrote that the McCormick dam and tunnel system “received its first heavy volume of water and is reported to have held the onrush perfectly, carrying a tremendous body of water through the heart of the business district to Pinal Creek in fine shape.”

Then and now

I have never seen it in action, but I can only imagine all that water rushing through the tunnel and exploding out into Copper Gulch just as Indiana Jones leaps to a thin edge outside the exit point, narrowly missing the gushing torrent.

In the Facebook Group, Growing up in Globe, Maude Medlin-Brown remembers something similar. She used to wait with her sister above the exit to the tunnel during storms. “You did NOT want to be in the exit path because huge rocks and debris shot out of the tunnel,” she wrote. 

The dam is not only close to town, it’s in town. The row of houses on Mesquite Street just below Copper Rim School are built on the left bank of McCormick Wash. Those residents just have to look down 25 feet from the edge of their back yard fence to see the dam. But what they see today is definitely not what it looked like nearly 100 years ago.

The dam has filled in to within 4 or 5 feet of the top with sediment that now supports a thick colony of riparian vegetation. When I was hiking in to it, I knew I was getting close when the vegetation got taller and lusher.  Subtract the decades of graffiti and the eroded concrete of the rather grandiose and ornate entrance to the tunnel, and it looks in pretty decent shape, but could definitely use some maintenance. The tunnel is clear all the way through with no major cave-ins.

The Copper Gulch side of the tunnel is surprising undeveloped, with no evidence of any concrete or masonry to stabilize the exit. It’s just a hole that opens into thin air. Over the years, the force of water has eroded away a deep chasm that runs to the floor of the gulch.

Getting there

McCormick Wash drainage channel west of hill Street on Sycamore. From here, the channel continues completely underground to Pinal Creek. Photo by Kim Stone

Even though the dam and tunnel are close to home, getting there takes some effort. The land surrounding the dam and tunnel is Freeport-McMoRan property, so if you decide to visit, keep that in mind.

You can easily get down into McCormick Wash from the lowest part of the Bull’s Eye trail at Round Mountain Park. Follow the wash down stream for about a third of a mile. It’s a brushy hike through a rocky creek bed, so be prepared. There may be other ways to access it from Copper Hills Road or other locations on the downstream side, but I can’t vouch for any of them.

The best place to view both Copper Gulch and the dam in McCormick Wash is from Giorsetti Park at the top of Tonto on Fifth St. The park sits atop the mountain that divides the two drainages, so there are clear views to both sides. 


Editor’s note:  In the summer issue of Globe Miami Times (July 2018), we’re planning to explore a few more tunnels. We’ll burrow our way through the folklore, the hyperbole, the legends, and the lore about hidden tunnels that some say exist under the streets of downtown Globe. Who knows if they really exist, and if they do, who used them and why?  Everyone has heard the stories, but now it’s time to dig a little deeper and get to the bottom of Globe’s purported underground network. Is it fact or fantasy – or some of both? We intend to get down and dirty in the quest for answers in this summer’s upcoming issue. 


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