by Patty Winter
Mount Diablo holds a special place in U.S. land surveying history. Rising among valleys east of San Francisco, its 3,849-foot peak is visible throughout the Bay Area. To the uninitiated, a mountain of such modest elevation might seem unremarkable in a state known for the snow-capped Sierra Nevada range. But precisely because it stands alone, with views that span wide swaths of the Golden State, Mount Diablo has captured the attention of explorers, sightseers—and surveyors.
When Congress passed the Land Ordinance of 1785, the U.S. General Land Office (now the Bureau of Land Management) began surveying the western fringes of the young country. GLO survey teams established meridian and base lines for the Public Land Survey System
that created land divisions. Many of those lines were able to create survey controls for multiple states from one mountaintop.
But when California joined the union in 1850, GLO surveyors realized that a single meridian and base line would not suffice. For one thing, California’s slanted shape meant that no one meridian line could run the entire length of the state. Also, it would take too long to survey the large, topographically complex state from a single point. GLO Deputy Surveyor Col. Leander Ransom was therefore authorized to establish as many points as he thought were required to cover California.
In 1851, Ransom began a survey at Mount Diablo. In the following two years, Mount San Bernardino was chosen as the initial point for southern California, and Mount Pierce in Humboldt County became the survey center for the northwestern corner of the state. But most of California, and all of Nevada—hundreds of thousands of square miles in all—became enduringly linked to this unassuming mountain near San Francisco.
As land surveyor John W. Pettley, a member of the Mount Diablo Surveyors Historical Society (MDSHS), described in Volume 12, Issue 3 of Berntsen’s Survey Log publication:
On July 18 of that year, in oppressive summer heat, Ransom labored through dense brush up the steep terrain to get to the top of the mountain. There he chiseled a hole 6 inches square and 9 inches deep in the solid rock on the highest point of the mountain, and erected a flagpole to be used as a sight to establish monuments on the base and meridian lines.
Deciding that it was too difficult to survey from the summit of the mountain, Ransom then went due south 12 miles and set additional monuments to establish the meridian line. He continued setting monuments due east, due north, and due west of the initial point on the summit of the mountain, thereby establishing the Mount Diablo Base and Meridian lines. Ransom completed his survey on August 31, 1851.
One year later, in 1852, R.D. Cutts of the United States Coast and Geodetic Survey traveled to the top of Mount Diablo on a mission to establish a survey marker for mapping surrounding waterways and topography. After finding Ransom’s initial point set a year earlier, Cutts established his monument [a drill hole in the rock] 3 feet to the southwest and 3 feet lower, on a flat ledge that was more suitable for setting up a tripod and survey instrument. He carefully noted the relationship of the two points in his official notes, and included a sketch showing their relationship to each other.
Over the years, however, confusion set in regarding the relationship between the two points. Some accounts stated that the two points were the same, and other accounts (including the Cutts account) stated that there were two separate points. One account even stated that the initial point was believed to be lost.
Up the mountain
This past June, some benchmark-hunter friends and I made a pilgrimage to Mount Diablo to see this historic location. Smoke and haze from large wildfires in northern California quickly put an end to any
hope of seeing the Sierra Nevada that day, but we weren’t deterred from our main goal. Michael J. Foley, P.L.S., of the MDSHS met us at the summit parking lot to give us a guided tour of Diablo’s surveying highlights.
The main attraction greeted us as soon as we walked into the tall, narrow building that houses a lookout tower and interpretive exhibits. We immediately faced an octagonal, hollow concrete pillar that rises into the room above and has a plaque discussing the Mount Diablo survey marks.
By kneeling on the floor and peering through an opening in the base of the pillar, you can see the top of a metal bolt. It marks the location of the Coast Survey station established by R.D. Cutts in 1852 (although the bolt itself was placed later).
Walk up a few stairs that curve around the pillar, and you get to part of the floor that’s been left open to expose a small rocky area. This is the actual summit of Mount Diablo—confined, but still wild.
Although Col. Ransom’s notes say that he chiseled a hole 6 inches square and 9 inches deep, nothing of those dimensions exists today. The only depression that looks manmade in the exposed portion of the rock is about 8 inches wide, 11 inches long, and an inch or two deep. Could this be Ransom’s initial point?
IP, or not IP?
That’s where the story gets tricky. John Pettley and many other surveyors are convinced that this exposed piece of rock is indeed Ransom's initial point, and that alteration of the rocky summit over the decades has greatly reduced the depth of the original hole he chiseled.
Other surveyors, however, are not so sure. C. Albert White, in his 1997 book, Initial Points of the Rectangular Survey System
(published by the Professional Land Surveyors of Colorado), argues that Ransom’s initial point is the same place where Cutts established the Coast Survey station. Did Cutts record events incorrectly when he said he drilled a hole three feet away from Ransom’s initial point? Was Cutts mistaken about the location of the initial point? Were Ransom’s reports based on his own actions atop Mount Diablo, or on the recollections of a tired crew member relaying the day’s events to him at base camp? With Ransom’s stated 6x6x9-inch hole no longer evident, the controversy may never be laid to rest.
What no one disputes is Mount Diablo’s ongoing importance to both land and geodetic surveying. The base line it establishes runs from the Pacific Ocean to the Nevada-Utah border. Its meridian line goes from Monterey Bay to the California-Oregon border. Cutts’ drill hole has become HS5120
in the NGS database—a first-order horizontal control station—and is one of the oldest California survey stations still in existence.
The Mount Diablo Surveyors Historical Society works assiduously to educate people about the mountain’s significance, and to preserve other aspects of California’s land surveying history. You can pick up their free flyer at the summit visitor center, or visit their booth at local festivals and commemorative events. And if you ever have a few spare hours when you’re in the Bay Area, consider making the drive up Mount Diablo. With luck, you’ll see some great views—and rain or shine, you can visit one of the most important survey points in the United States.
Patty Winter is the contributing editor of Caching Now. A freelance writer based in the San Francisco Bay Area, she writes marketing materials for high-tech companies, and magazine articles about science and technology.
All photos (c) 2008 Patricia F. Winter.
Originally published on August 13, 2008.