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  • Writer's pictureDale Hill

Mount Diablo Initial Point

Updated: Sep 8, 2023

SMASH Statistics (Mt Diablo SP)

Recovery Date: August 19, 2023

Total Marks Recovered: 8

Confirmed Lost/Destroyed: 1

Discs Recovered: 2

Non-Disc Type Recovered: 5 (CORS GRM, Bolt, Memorial Plate, Pipe Cap, Chiseled Hole)

I recovered 49 survey marks over the week, hiked Mount Diablo, biked across the Golden Gate Bridge, and toured Sausalito and The Presidio of San Francisco by bike. This article will focus on the eight survey marks I found in Mount Diablo State Park, specifically, the Mount Diablo Initial Point.

View looking north from the observation deck of the Mount Diablo Light

The "Birthday Week Plan"

Last year, I celebrated my birthday week in the Eastern Sierra, camping, looking for survey marks, and topping it off with a 3-day backpacking trip to summit Mount Whitney (my first time!) This year, I wanted to do something similar; however, given my recent ACL reconstruction surgery, my surgeon gave me the green light for hiking, but with the following conditions:

  • Stick to fire roads and improved trails.

  • Avoid Class III scrambling and climbing.

  • No running, cutting, or quick change of direction.

  • And in general, watch my footing.

I decided to flip the script from last year, where backpacking and summiting Mount Whitney was the main focus of my trip; this year, my primary focus was searching for survey marks. Given that survey marks would take center stage, I needed something big, a worthy objective to build a week-long trip around. 🤔

The answer: the Mount Diablo Initial Point, the first Initial Survey Point established in California in 1851.

Proposed Itinerary

With Mount Diablo as my focal point, I researched the surrounding area for other points of interest and potential survey mark recoveries and prepared a rough itinerary for my trip. As it turned out, my plan was solid, and I followed it to the letter!

  1. Saturday, 8/19/2023: Drive from Ramona to Mount Diablo State Park and recover all survey marks at the summit. There were no available campgrounds within a reasonable difference, so I booked a hotel in nearby Concord.

  2. Sunday, 8/20/2023: Return to Mount Diablo to hike the Summit Trail. Booked campground for the next three nights at China Camp State Park. This would be my "home base" for the remainder of my time in the Bay Area.

  3. Monday, 8/21/2023: Spend the day at Angel Island State Park, rent a mountain bike to tour the Island and look for survey markers.

  4. Tuesday, 8/22/2023: Visit Sausalito and the Presidio of San Francisco; ride my beach cruiser around looking for survey marks. Birthday dinner in Sausalito. 🦀😋🎂

  5. Wednesday, 8/23/2023: Return home, stop, and look for selected survey marks on the drive home.

Quik-Navigation Shortcuts

Public Land Survey System (Overview)

The U.S. Public Land Survey System (PLSS) was created to subdivide and describe federal land west of the Ohio River Valley. The PLSS was proposed by Thomas Jefferson and enacted into law by the Land Ordinance of 1785. Often referred to as the Rectangular Survey System, it divided the country into a grid of Townships, each 36 square miles. The townships were divided into 36 one-square-mile sections, which could be further subdivided.

  • Section: 640 acres

  • Half Section: 320 acres

  • Quarter Section: 160 acres

  • Half Quarter Section: 80 acres

  • Quarter-quarter Section: 40 acres

Sections can be divided in multiple ways; for simplicity, the graphic below shows dividing a section into quarters and further dividing each quarter into quarter-quarters.

In 1812, The U.S. Congress created the General Land Office (GLO) to handle the increasing need to survey public land, administer its sale, and document the transactions. The GLO performed cadastral surveys to define and mark the boundaries of townships and sections as the U.S. expanded westward. Public land surveyed for the PLSS is identified by its legal description, the primary components being state, principal meridian, township, range, and section.

In 1946, the GLO merged with the Grazing Service and formed the Bureau of Land Management (BLM). The BLM maintains all the records for more than 200 years of title and survey records, searchable on the U.S. Department of Interior, Bureau of Land Management, General Land Office Records website.

There are 37 Principal Meridians in the United States; these main north/south lines are used for surveying large regions. For a land survey, the point where the principal meridian bisects its baseline (east/west line) is the Initial Point.

The initial point may be preselected based on a distinct geographical feature, as with the Mount Diablo meridian, selected because the summit could be seen from miles around and was a good reference point for surveys. Some initial points were chosen based on existing markers. The initial point for the Gila and Salt River meridian was established based on an existing marker set up in 1851 to mark a point on the Mexico–United States border before the Gadsden Purchase. Others have historical significance, like the Beginning Point of the U.S. Public Land Survey, which is the point from which the United States in 1786 began the formal survey of the lands known then as the Northwest Territory, now making up all or part of Ohio, Indiana, Illinois, Michigan, and Wisconsin. That initial point is underwater, but a monument commemorates it on the Ohio River's north side.

California Initial Points

When the Mount Diablo Initial Point was established in 1851, it was intended for it to be the only one in California; however, due to the size of the state, two additional initial points were added: San Bernardino, established in 1852, and Humboldt, established in 1853. As depicted in the BLM map below, the Mount Diablo Initial Point is the basis for most property boundaries in Northern California and all of Nevada.

California Principal meridians. (2023, June 30). In Wikipedia.

Mount Diablo Summit Building

Mount Diablo has the most elaborate commemorative architecture protecting the initial point of the 37 federal Initial Points (outside the original 13 colonies).

Pictured above are two views of the Mount Diablo Summit building; the first floor provides access to the Initial Point and a U.S. Coast and Geological Survey Triangulation Station, the second floor has a memorial brass plaque mounted on the top of the concrete pillar built over the triangulation station, and the third floor (not open to the public) has access for surveyors to set their equipment above the Triangulation Station. However, since the memorial plaque was permanently mounted in 1987, there is no access to the bolt from the third floor.

The Civilian Conservation Corps (CCC) constructed the elaborate Summit Building that now houses the initial point during the 1930s; built from stone quarried in the Park, the rock

used in it contains fossils of sea creatures that are millions of years old! The CCC design of the building, "rustic park architecture," became a standard for the California State Park System. However, the building had significant water intrusion problems that took over 40 years to address fully. The building now houses a museum, visitor center, survey marks, and observation deck.

There are four survey marks located inside the Mount Diablo Summit building: the Initial Point, the USC&GS Triangulation Station MOUNT DIABLO (PID: HS5120), plus MOUNT DIABLO RM1 (PID: DB2637) & RM2 (PID: DB2638). Both reference marks are located on the third floor and are not accessible to the general public. In addition to the survey marks, a memorial brass compass rose is mounted at the top of the concrete pillar above the Triangulation Station. Not a survey marker, it is a notable feature in the Mount Diablo Summit building.


Colonel Leander Ransom, Deputy Land Surveyor of the United States Bureau of Land Management (BLM), established the initial point atop Mount Diablo in 1851, soon after California was admitted to the Union. The peak's highest elevation is 3,849 feet, and the view from the summit is incredible. According to Park history, it is estimated that you can see more than 40,000 square miles from the summit, including 35 of California's 58 counties. This unimpeded view was a driving factor behind establishing the initial point on Mount Diablo.

As you can see in the photos above, the actual summit of Mount Diablo is accessible from inside the building, worn smooth by foot traffic over the years; you can still make out a faint rectangular depression in the rock that is the initial point. Colonel Ransom described the initial point as

"a hole six inches square and nine inches deep in the most prominent peak of Mount Diablo."

After preparing the hole, he placed a staff (28 feet high) and a flag (9 feet long and 4 feet wide) that could be seen from below as he continued the survey.

It amazes me that he climbed this mountain in 1851, packing survey equipment, tools, provisions, etc., cutting a six-inch square hole nine inches deep in the summit bedrock, then fashioning a 28-foot flagstaff and mounting it in the hole he prepared. Amazing.

After establishing the initial point, he moved 12 miles due south of the flag and began his survey of the meridian and base lines there. The steep terrain around the summit made running lines directly from the initial point difficult. From here, he began working outward, identifying and marking township corners.


Due to its prominent location, Mout Diablo has been used by various state and federal agencies for important horizontal control monuments. One of the first marks on the mountain was a tower and airway beacon built by Standard Oil Company. History has it that Charles Lindberg lit the airway beacon! That tower is gone, but the airway beacon light now sits atop the Mount Diablo Summit building and is lit every year on December 7, commemorating Pearl Harbor Remembrance Day.

In 1852, R.D. Cutts of the U.S. Coast and Geodetic Survey (USC&GS) established a first-order Triangulation Station, MOUNT DIABLO, on the most easterly side of the summit, just feet away from Colonel Ransom's initial point. The initial Station description was described as "a hole about 2 inches in diameter and 1 ½ inches deep in the center and bottom of another hole inches in diameter and 6 inches deep."

Five additional recoveries of the Station were reported between 1852 and 1935; in 1876, a copper bolt was added to mark the Station. Brick and concrete piers were noted in various stages of disrepair. During the 1946 recovery of the station, it was noted that the new building had been built around the mark, and a tapered, octagonal concrete pillar (hollow in the center) was built above the bolt, with access holes on either side. A 10-inch diameter pipe in the center of the pillar afforded access from the third floor of the building.

At one point, there was confusion about the copper bolt; was it the initial point? However, a local Land Surveyor (John W. Pettley) researched all available records and conducted a field investigation and survey at the Summit of Mount Diablo to clarify, once and for all, the nature of the two marks at the summit. The illustrations accompanying my photographs are from his paper: The Re-discovery of the Mount Diablo Initial Point, Surveying and Mapping, Volume 48, No. 2, June 1988.

Just as Colonel Ransom's field notes confirmed the location of the initial point, R.D. Cutts's notes clearly identified the Triangulation Station he set as a separate and different mark:

"The highest rock on the summit has been selected as the starting point for the survey of Public Lands in California. in a S 20º W direction from the above mentioned [sic] rock, and three feet below its level and three feed distant is the Coast Survey Station."


This mark did not have PID assigned; measurements confirmed the location and narrative descriptions referenced in the DIABLO ECC RM 2 1962 datasheet.

DIABLO ECC RM 2 1962 (PID: HS5373)

There were two discs labeled DIABLO ECC RM 2 listed in the datasheets: one dated 1961 and this one. I could not locate the 1961 disc, remains of the stem, or evidence of its mounting location in the rock as described. This reference mark is located on the sidewalk and is in good condition.


This Azimuth Mark was added in 1946 and is about a half-mile from the Triangulation Station. Finding Azimuth Marks can be challenging because the datasheets rarely provide exact coordinates, giving only the geodetic azimuth heading from the Station and a brief "to reach" description. This was not too far from the main road and near a power pole referenced in the datasheet.


This plaque is not a survey mark but a notable feature in the Mount Diablo Summit building. Placed in August 1987, finding any information about the memorial online was difficult. I emailed the Mount Diablo Interpretive Association (MDIA) Sunday morning (9/3/2023) asking for any information about the compass rose mounted on the top of the concrete pillar in the summit building. Later that afternoon, I received a response that included images of two pages from the MDIA publication Mountain Lore. (Available on the association's website; I purchased this book and a copy of the Mount Diablo Hiking Guide. 😊)

Lt Col Norman Edward Denning (1911-1983) and his wife Frances Jean [nee Warner] Denning (1913-1984) were frequent visitors to Mount Diablo State Park. They were avid Park equestrians who lived in the nearby town of Diablo. Norman was a highly decorated Marine Corps officer and aviator. Frances' great uncle, Thorburn "James" Cumberpatch, who was also an aviator, puportedly played a role in establishing the Standard Oil aviator navigation beacon on top of Mount Diablo in 1928.

Upon the death of their parents, the Denning children commissioned the plaque. The bronze compass was chosen because of the family's involvement with aviation and the beacon. The plaque was cemented to the top of the pillar, replacing a removable metal plate that provided access to the Triangulation Station on the first floor. Local stone was added around the plain concrete pillar. The work on the Denning Compass was completed in January 1997. If you look closely at the compass, the base and meridian coordinates are engraved on the plaque above and below the center image of the mountain. Before the plaque's installation, surveyors could access the copper bolt set in 1852 from the third floor through a hole in the floor and by removing the steel plate from the pillar on the second floor, revealing the concrete pillar's 10-inch diameter pipe centered above the bolt on the first floor.


This Continuously Operating Reference Station, Geodetic Reference Mark (CORS GRM), is located just below the Summit Trail at about 3,337 feet and 0.6 miles before reaching the summit. The NOAA/National Geodetic Survey manages these stations, which provide Global Navigation Satellite System (GNSS) data, supporting three-dimensional positioning, meteorology, space weather, and geophysical applications throughout the United States.

The CORS network is a multi-purpose, multi-agency cooperative endeavor, combining the efforts of hundreds of government, academic, and private organizations. The stations are independently owned and operated; Scripps Institution of Oceanography owns this station. Each agency shares its GNSS/GPS carrier phase and code range measurements and station metadata with NGS, which are analyzed and distributed free of charge.


This PLSS pipe cap marker identifies the NE corner of the SENE Quarter-quarter of Section 14. This was the first marker I found within the Park today. It is next to a restroom facility just off Little Rock City Road, across from the Big Rock Picnic Area. The plain cap with a cross on the top is cool, even without engraved markings.


After a full day of driving from Ramona to the summit of Mount Diablo, I had a good time hanging out at the summit, checking out the visitors center and museum, then looking for all the survey marks on my list.

As is often the case, some previously identified survey marks are no longer there. The MOUNT DIABLO AVIATION BEACON (PID: HS5122) is technically gone. The light from the original steel tower erected in 1928 by the Standard Oil Company is now mounted atop the Mount Diablo Summit Building, and some erroneously report the light in its current location as the survey mark. However, HS5122 is officially marked as destroyed in the NGS database, and there is no geodetic control tied to the current position of the light. In historical photos of the summit, you can plainly see a large flagpole; however, the MOUNT DIABLO FLAGPOLE (PID: HS5119) no longer exists at the summit; its original location was 16 feet NNW of the Triangulation Station (copper bolt now inside the summit building). It was likely removed during the construction of the new summit building.

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