Corner Types & Monuments

Overview#

The PLSS is defined on the ground by its corners -- the specific points that mark the intersections and midpoints of section lines, township boundaries, and other surveyed lines. These corners are the highest form of boundary evidence in the system. Every boundary, every legal description, and every acreage calculation in a PLSS state ultimately depends on the position of the original corners established by the government surveyor.

A critical distinction that every surveyor must understand is the difference between a corner and a monument. The BLM Manual defines these terms precisely, and confusing them leads to errors in both fieldwork and legal interpretation.

"The terms 'corner' and 'monument' are not interchangeable. A 'corner' is a point determined by the surveying process. A 'monument' is the object or the physical structure that marks the corner." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-8

Corner vs. Monument#

The Corner

A corner is a point on the Earth's surface whose position was determined by the surveying process. It exists as a legal concept -- the point where two or more boundary lines intersect, or the point that controls the position of a boundary line. The corner exists whether or not a physical marker is present at the location.

"The 'corners' of the public land surveys are those points that determine the boundaries of the various subdivisions represented on the official plat -- the township corner, the section corner, the quarter-section corner, the subdivision corner, or the meander corner." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-9

The Monument

A monument is the physical object placed at a corner to mark its location. Over the history of the PLSS, monuments have taken many forms:

"Monuments of the public land surveys have included the deposit of some durable memorial, a marked wooden stake or post, a marked stone, an iron post having an inscribed cap, a marked tablet set in solid rock or in a concrete block, a marked tree, a rock in place marked with a cross (X) at the exact corner point, and other special types of markers." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-10

The monument may be destroyed, displaced, or obliterated, but the corner -- the legal point -- still exists at its original position. The surveyor's task in retracement is to recover the corner, using whatever evidence of the monument, its accessories, or its position remains.

Not All Corners Are Monumented

Many corners in the PLSS were never physically monumented. Quarter-quarter section corners and sixteenth-section corners were often protracted on the plat without a monument being set on the ground. The 2009 Manual notes:

"Not all corners of the Federal surveys are monumented. Many unmonumented corners were subsequently monumented during official resurveys, or by county or other local surveyors." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-10

Standard Corner Types#

Township Corners

Township corners are established at the intersection of township lines. A corner common to four townships is the highest-order corner in the subdivision of a survey area. Township corners are established at intervals of 480 chains (6 miles) along the principal meridian, baseline, standard parallels, and guide meridians.

Section Corners

Section corners mark the intersections of section lines within a township. A standard section corner is common to four sections. Section corners are established at intervals of 80 chains (1 mile) along the section lines.

Quarter-Section Corners

Quarter-section corners are established at the midpoint (nominally 40 chains) of each section line. They divide the section boundaries into halves and, when connected across the section, define the four quarter sections.

Quarter-section corners are the most common monumented points that local surveyors encounter. The line connecting opposite quarter-section corners establishes the centerline of the section, and their intersection defines the center of section.

Sixteenth-Section Corners (Subdivision-of-Section Corners)

Sixteenth-section corners are established at the midpoint of each quarter-section boundary (at 20 chains from the quarter-section corner). They define the boundaries of the quarter-quarter sections (40-acre parcels). In many original surveys, these corners were protracted rather than monumented, and local surveyors later established them on the ground.

Special Corner Types#

Closing Corners

A closing corner is established at the point where a surveyed line meets (closes on) a previously established line. The closing corner falls on the previously established line. It is not a corner of the sections on both sides of the line; it refers only to the sections on the side from which the closing line was run.

Closing corners are common on the south and east boundaries of townships, where subdivision lines close on the previously established township exterior or standard parallel. The distance between the closing corner and the nearest standard corner on the established line is the "closing distance," which measures the accumulated error.

"A lost closing corner will be reestablished on the true line that was closed upon, and at the proper proportional interval between the nearest regular corners to the right and left." -- BLM, Manual of Surveying Instructions (2009), Sec. 7-41

Meander Corners

A meander corner is established where a surveyed line (section line, township line, or standard parallel) intersects the ordinary high water mark (OHWM) of a meanderable body of water. It is not the boundary of the upland parcel -- the actual boundary is the water's edge -- but it is a controlling monument on the surveyed line and has the authority of a corner of first order.

"Although considered an intermediate monument, it is actually a corner of first order. The actual boundary of the meandered body of water is the ordinary high water mark or the line of mean high tide. Meander corners are set to delineate acreage, not to mark the boundary with the water body." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-30

Witness Corners

A witness corner is a monumented point established on a line of the survey, near the true corner point, when the true point is in a location where a durable monument cannot be established or would be destroyed. Common situations requiring witness corners include corners that fall in water, in a road, on a steep cliff, or in unstable ground.

"A witness corner is not the corner point but a witness to the true point for the corner. The corner point being witnessed is recovered when the witness corner is recovered." -- BLM, Manual of Surveying Instructions (2009), Sec. 6-27

The witness corner is connected to the true corner by a measured bearing and distance recorded in the field notes. To recover the true corner, the surveyor locates the witness corner and applies the record bearing and distance.

Reference Monuments

A reference monument is a special-purpose monument established near a corner to perpetuate the corner's position when the corner itself is vulnerable to destruction. Unlike a witness corner, a reference monument is not necessarily on a line of the survey. It is connected to the corner by a measured bearing and distance.

Angle Points

An angle point marks a change in the bearing of a surveyed line. It is a corner of the survey in the sense that it defines the direction of the line, but it does not mark the intersection of two section or township lines. Angle points are common on reservation boundaries, grant boundaries, and other special survey lines.

Monument Specifications#

Historical Monuments

The physical form of monuments has evolved dramatically over the 200+ year history of the PLSS:

Modern Requirements

Under the 2009 Manual, corner monuments must be:

• Permanent -- constructed of durable materials that will withstand the local environment.
• Marked -- inscribed with information identifying the corner (township, range, section, corner type).
• Set at the exact corner point -- the monument marks the precise legal corner.

"Monumentation establishes a permanent marking of the lines and fixes the corner positions so that the location of the surveyed lands may always be definitely known." -- BLM, Manual of Surveying Instructions (2009), Sec. 4-1

The Legal Significance of the Monument

The monument set by the original surveyor carries the highest legal significance. It is the physical evidence of the federal government's decision about where the boundary is located. Courts have consistently held that the original monument controls over courses, distances, and computed areas when there is a conflict.

"A cadastral/official survey is the highest form of boundary evidence available to the Federal Government, providing legal evidence of the geographic limits of the Federal interest in land." -- BLM, Manual of Surveying Instructions (2009), Sec. 1-5

This principle means that a surveyor who finds an original monument must accept its position, even if modern measurements show that the monument is not where the field notes indicate it should be. The monument is where the corner is -- the field notes describe the monument, they do not define its position independently of it.

Marking System

Monuments are marked according to a systematic scheme that identifies the corner type and its position in the township grid. The marks are inscribed on the monument (on iron post caps) or scribed on stone monuments. The marking system includes:

• Township and range numbers
• Section numbers (for the sections cornering at the monument)
• Corner type designation (SC for standard corner, CC for closing corner, MC for meander corner, WC for witness corner, etc.)
• Directional grooves on the cap pointing along the surveyed lines

Corner Accessories#

Purpose

Accessories are physical objects established near a corner monument to evidence its position. If the monument is destroyed, the accessories provide the means to recover the corner's location.

"The purpose of an accessory is to evidence the position of the corner monument. A connection is made from the corner monument to fixed natural or artificial objects in its immediate vicinity, whereby the corner may be relocated from the accessory." -- BLM, Manual of Surveying Instructions (2009), Sec. 4-79

Types of Accessories

Bearing Trees

Bearing trees are among the most important accessories in wooded areas. Each bearing tree is described in the field notes with:

• Species of tree
• Diameter at breast height
• Exact direction (bearing) from the monument to the center of the tree
• Horizontal distance from the monument to the center of the tree at its root crown
• Marks scribed on the tree

"Bearing trees are selected for marking when available, ordinarily within a distance of 3 chains of the corner; a greater distance if important. One tree is marked in each section unless a tree in one or more positions may not be available." -- BLM, Manual of Surveying Instructions (2009), Sec. 4-81

Trees are marked on the side facing the monument, with the marks reading downward ending in "BT" approximately 6 inches above the root crown. Sound, young trees of hardy species are preferred over mature trees showing decay.

The Permanence Requirement

The BLM Manual emphasizes that the surveyor's duty to establish permanent evidence of the corner cannot be overstated:

"The surveyor cannot perform any more important service than that of establishing permanent and accurate evidence of the location of the corners of a survey. Where the accessories cannot be employed, other means should be adopted that will best serve the purpose." -- BLM, Manual of Surveying Instructions (2009), Sec. 4-80

Summary Table of Corner Types#

Key Takeaways#

• A corner is a legal point; a monument is the physical marker. The corner exists at its original position whether or not the monument survives.
• Township corners and section corners are the highest-order control points. Quarter-section corners subdivide section boundaries; sixteenth-section corners subdivide quarter-section boundaries.
• Closing corners are set where a line meets a previously established line. They refer only to sections on the approaching side.
• Meander corners are set where survey lines intersect the OHWM of navigable water. They are corners of first order, though the actual boundary is the water's edge, not the meander line.
• Witness corners mark a point near the true corner when the corner itself cannot be monumented. The true corner is at record bearing and distance from the witness corner.
• Accessories (bearing trees, bearing objects, mounds of stone, memorials, pits) provide evidence of the corner's position if the monument is destroyed. They are an essential part of the corner record.
• Modern monuments are aluminum or brass-capped iron posts. Historical monuments include wooden stakes, marked stones, and marked trees -- all of which may still be encountered in retracement surveys.
• The permanence of corner evidence is the surveyor's paramount responsibility.

References#

1. U.S. Department of the Interior, Bureau of Land Management. Manual of Surveying Instructions (2009). Chapter IV: Monumentation, Secs. 4-1 through 4-112. Chapter VI: Resurveys and Evidence, Secs. 6-8 through 6-30.
2. U.S. Department of the Interior, Bureau of Land Management. Restoration of Lost or Obliterated Corners and Subdivision of Sections. Manual Supplement.
3. U.S. Department of the Interior, Bureau of Land Management. Glossary of BLM Surveying and Mapping Terms. Manual Supplement.
4. Robillard, W.G., Wilson, D.A., & Brown, C.M. Brown's Boundary Control and Legal Principles (7th Ed.). John Wiley & Sons, 2014. Chapter 18.