EXPLANATIONOF COLUMNS ON BENCH MARK LISTING
1. BENCH MARK DESIGNATION. - This column indicates the number, name, or letter designation of the Bench Mark.
2. QUAD SHEET. - This column indicates the number of the seven and one-half minute U.S.G.S. Quad Sheet in which the Bench Mark is located. See Page VI for quad name listing.
3. ESTABLISHING AGENCY, HORIZONTAL & VERTICAL. - This column indicates the Agency, by code number, that established the horizontal coordinates or vertical elevation. See Page V for explanation of codes.
4. COORDINATE INDEX. - Record coordinates are listed if available; otherwise the coordinate is listed to the nearest 1,000 feet, scaled measurement. Coordinates are based on California Coordinate System Zone 6, NAD 27.
5. IDENTIFIER STREET. - Name of street or road on which Bench Mark is located, or street or road nearest to the Bench Mark.
6. TWP-RAN-SEC CITY OR GRANT. – This is the Township, Range, Section, City or Grant in which the Bench Mark is located. Example: T17R4E07 would mean Township 17 South, Ranch 4 East, Section 7. All Townships in San Diego County are South. If not sectionalized, the Branch Marks are listed by Rancho or Area location. See Page X for abbreviations.
7. ELEVATION. - This is the elevation established for the Bench Mark, based on the National Geodetic Vertical Datum of 1929. All elevations shown on the listing are shown to the nearest thousandth of a foot, even though actual elevations may have been carried out to the nearest hundredth of a foot. Zeros were added to make all elevations uniform on the listing. All elevations are subject to future adjustments.
8. ORDER, HORIZONTAL AND VERTICAL. - Order of work Indicated by the agency that established the elevation and/or position of the Bench Mark. See Page V for code explanation.
9. MONUMENT TYPE. (A TWO LETTER CODE.) – Left letter indicates agency which built the monument. Right letter describes the physical characteristics of the monument. See Page V for code explanation.
HOW TO USE THE BENCH MARK LISTING
For the purpose of convenience and because of the vast number of Bench marks within the County, it has been necessary to list the Bench Marks in two different books. One is called the "North County Vertical Control Data" book and the other is the "South County Vertical Control Data" book. The South County book contains information on Bench Marks covered by the area included on Page VII. The North County book is covered by the area included on Page VIII.
Each book is divided into sections. The first section is a listing with descriptions of all Bench Mark designations listed alphabetically and numerically. The second is a listing of all Bench Marks within a U.S.G.S. seven and one-half minute quadrangle; and these will be arranged alpha-numerically according to identifier-street name and then alpha-numerically by Bench Mark designation. The County of San Diego is divided into eighty-six, seven and one-half minute quadrangle areas. Each quadrangle is Named; i.e., "Point Loma," "El Cajon", "Escondido," etc. Each quadrangle is numbered 1 -86 inclusively. See Pages VI thru VIII.
The third section is a listing of each Bench Mark by its coordinates. The coordinates will be listed from west to east in horizontal order, starting at the southernmost coordinate and rising one thousand feet at a time northward to the northernmost coordinate.
EXAMPLE: 180,000.000 - 1,700,000.000
180,000.000 - 1,720,000.000
181,000.000 - 1,680,000.000
The fourth section is a listing of identifier-streets listed alpha-numerically. Bench Marks that are on or near each identifier-street listed alpha-numerically.
EXPLANATION OF STATE COORDINATE SYSTEM
The coordinate positions included in this book conform to the system of Plane Coordinates which has been established by the National Oceanic and Atmospheric Administration for defining and stating positions or locations on the surface of the earth within the State of California. This system is known as the "California Coordinate System."
For This system, the state has been divided into Seven Zones. San Diego County, along with Imperial, Orange and Riverside Counties, falls in Zone 6, so these four southernmost Counties share the same point of origin for their coordinate system. This makes it easy to relate locations of all points falling in these four counties.
The origin point for Zone 6 (Zero N, Zero E) lies about 35 miles south and 321 miles west of the tip of Point Loma, and all locations are given so many thousands of feet north and east of the Zero N and Zero E point.
The small numbers along the left, top and bottom edges of the maps, Pages VII and VIII, are coordinate values (in thousands of feet) of the northsouth and eastwest grid lines. Grid lines are spaced 20,000 feet apart on the maps. Northsouth coordinates have values in the hundred thousands and the eastwest are in millions, e.g., 240 means 240,000 feet north of the Point of Origin and 1740 means 1,740,000 feet east of the Point of Origin.
Each Bench Mark has been assigned coordinates. In most cases the coordinates have been scaled to the nearest thousand feet. Where actual coordinates have been established they are shown to the nearest one-thousandth of a foot. As actual coordinates are established or readjustments are made on existing coordinate values they will be placed in the book.