Earthquakes Shaped The Rim Country Landscape

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Rim country residents tend to feel smug about natural disasters, we have so few of them here in Arizona central mountains. While earthquakes, tornadoes, avalanches, mudslides, tidal waves and hurricanes batter nearly every part of our nation at one time or another, we seem free from such fearsome events.

Well, except for fire and drought. Fires are something we are learning about through hard experience, hoping for more enlightened management of our forests.

Drought? We are beginning to realize that most of us came here during a wet period. We expected it to continue, but that is because we did not know the history and pre-history of the region. (See my article on "Learning to live with our fickle weather" in the Roundup July 9, 2002.)

But what about earthquakes? Surely these majestic mountains around us did not get here peacefully. The mountains that separate us from the Valley seems small enough as mountains go.

The Mazatzal range is 7,903 feet at its highest and nearly 50 miles from end to end, the longest in our state. It is honeycombed with hiking trails and jeep roads, once plied by prospectors and mule trains. The southern high point is the famous Four Peaks, once sacred to pre-historic people. Coming from the south, one speculates how the Indians saw that magnificent symbol of their faith rising on the horizon, and said to one another like some ancient Joseph Smith, "This is the place." They set up camp, multiplied, and became the people we call the Hohokam.

Eons before them the faults bounding the Arizona ranges were active. A vast area from southeastern Oregon through Nevada, western Utah, parts of eastern California and into southern Arizona was involved in a great uplifting.

What we know as the Sierra Ancha, Pinal and Mazatzal mountains formed one huge range that was 30,000 feet high. At that time, there was no Mogollon Rim, and the Colorado plateau spread out from the base of the mountain. The uplifting created fractures along which the basins and valleys dropped. After that was over, the mountains began wearing down sending their alluvial material into the valleys. So the valleys filled as the mountains wore down, and that process continues today.

One would think there are still active faults to give us a shaking here in the Rim country, yet all the modern earthquake activity is from Flagstaff north. In 1906 there was a moderate quake in Flagstaff. In 1910 and again in 1912, there were quakes at the Grand Canyon. With the sensitive equipment of recent decades, frequent small tremors, on a scale of from one to three, are detected around the Grand Canyon area, but the Payson basin area seems to be completely calm. The escarpment of the Mogollon Rim looks as though it might be a giant fault line, and the country north of it rising. Not so. The Rim is caused by erosion, the Colorado plateau being eaten away by the weather and running water. We live in the piedmont, those hills at the foot of that ancient giant range that are still being eroded away.

The closest our Rim country came to feeling an earthquake in historic times was 115 years ago. It was a little after 2 p.m. in 1887. The Pleasant Valley War was brewing throughout the Rim country, and the recent influx of cattle ranchers was settling in to ravage the grasses and forests. Those man-made catastrophes seemed small compared to the earthquake that let go near Bavispe, Sonora, where a 75 kilometer rupture occurred in the earth's surface. It is estimated to have been between 7.2 and 7.5 on the Richter scale. Hundreds were killed in Sonora, whole villages destroyed, and the shock waves carried over 400 miles.

In Tombstone, it sounded like dynamite exploding and the earth shook violently, sending merchandise from the store shelves.

In Charleston, along the San Pedro River, every building was damaged by the quake that rattled for over 30 seconds. Water gushed from fissures in the earth; spring-fed streams stopped flowing in some places. From Yuma to Tucson buildings shook, walls cracked, windows shattered, and clocks stopped. Rocks crashed down the mountainsides, and a cloud of dust hung over the Catalina Mountains so that Tucsonans erroneously reported a volcano had blown the crest.

When the tremor reached Globe it stopped the clocks at 3:11 p.m. Goods tumbled from store shelves and the townspeople fled from their homes into the streets. Everywhere in Arizona miners feared cave-ins and rushed to the surface. On the San Carlos reservation the shock created much excitement among the Apaches. Many abandoned their homes and fled to higher mountain elevations, fearing a great flood. With the Apache wars so recently ended a new fear now gripped the populace. Was this the new terror? However, it turned out to be a singular event. Scientific studies have indicated that such quakes on that fault recur about every 300,000 years. Before the 1887 quake the previous one had been at least 100,000 to 500,000 years earlier. So much for earthquakes here about, but what of other natural disasters?

Next week we will consider what manner of catastrophe could we face in the Rim country, beside fire and drought.

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