Section Corner

A section corner is a corner at the end of a section boundary in the Public Land Survey System (PLSS). BLM's Glossary of Surveying and Mapping Terms defines it simply as "a corner at the extremity of a section boundary." Most section corners are common to four sections.

How section corners are laid out

Federal law sets the pattern. A township is divided into 36 sections "containing, as nearly as may be, six hundred and forty acres each, by running parallel lines through the same from east to west and from south to north at the distance of one mile from each other, and marking corners at the distance of each half mile" (43 U.S.C. 751). Sections are numbered from 1 in the northeast corner of the township, back and forth to 36 in the southeast.

Related corners

• Quarter-section corner: "a corner at an extremity of a boundary of a quarter section," normally halfway between section corners
• Standard corner: a corner set on a base line or standard parallel. The Manual of Surveying Instructions calls the corners first set on a correction line "standard corners"
• Closing corner: set where a survey line meets a previously fixed boundary. By law it sits "at the actual point of intersection without regard to its monumented location" (BLM glossary)
• Meander corner: set where a section or township line meets the ordinary high water mark of a navigable stream or other body of water large enough to be meandered

What a BLM monument looks like today

Under the 2009 Manual (section 4-8), current regulation posts are 2.5 inches in diameter, set to three-fourths of their length, and made of stainless steel with a brass cap, aluminum with an aluminum cap, or zinc-coated iron with a brass cap. The cap carries the township, range, and section numbers, is read from the south, and shows the year it was set. Older corners may be stones, wooden posts, mounds, or marked trees.

Original corners control

By statute, the corners marked in the original survey "shall be established as the proper corners of sections, or subdivisions of sections, which they were intended to designate" (43 U.S.C. 752). The Manual adds that original corners stand as true corners "even though not exactly where professional care might have placed them in the first instance."

Existent, obliterated, and lost corners

• Existent: the original position can be identified by substantial evidence of the monument, its accessories, the field notes, or reliable testimony
• Obliterated: no trace of the monument remains, but its position can be recovered from other acceptable evidence
• Lost: the original position cannot be determined by substantial evidence. A lost corner is restored by proportionate measurement from the surrounding corners.

Why it matters for mining claims

Mining claim locations, maps, and mineral surveys are tied to section corners. Arizona, for example, requires the location map to tie to a PLSS corner or other permanent monument. When a corner has been lost and restored, or where two sets of corners exist along a standard parallel, the tie and the ground it describes need checking against the official plat and field notes.