Quarter Corner

A quarter corner, formally a quarter-section corner, is a surveyed corner on a section line at the end of a quarter-section boundary. BLM's Glossary of Surveying and Mapping Terms defines it as "a corner at an extremity of a boundary of a quarter section" and notes that it is "written as ¼ section corner." Most quarter corners sit halfway between two section corners.

Where the law puts them

Federal law directs that townships be divided into sections by lines a mile apart, "marking corners at the distance of each half mile" (43 U.S.C. 751). Where quarter-section corners were not marked in the survey, they "shall be placed as nearly as possible equidistant from two corners which stand on the same line" (43 U.S.C. 752).

BLM's Manual of Surveying Instructions (2009) sets quarter-section and section corners "alternately at intervals of 40 chains" along the section lines (section 3-52). Forty chains is half a mile. The exceptions are on the north and west sides of a township:

• In the north tier of sections, quarter corners are set 40 chains from the south, so "the excess or deficiency in measurement is incorporated in the north half mile" (section 3-54)
• In the west range of sections, they are set 40 chains from the east, putting the excess or deficiency in the west half mile (section 3-57)
• On the other east-west section lines, they are set at the midpoints (section 3-56)

What they control

To divide a regular section into quarter-sections, the Manual says to "run straight lines from the fixed quarter-section corners to the opposite corresponding quarter-section corners." The point where those lines cross is "the legal center of the section" (section 3-114). Every quarter-section and quarter-quarter boundary inside the section depends on the four quarter corners.

How they are marked

Quarter corner monuments carry the fraction "¼" with the section number, and a standard quarter corner on a standard parallel also carries "SC" (Manual sections 4-36 through 4-38). Bearing trees at a quarter corner are marked with "¼" and the section, for example "¼ S16 BT" (section 4-93 and following).

Double corners and lost quarter corners

Where there are two sets of section corners on a township or range line, the Manual notes that certain quarter corners "historically were not marked in the original surveys," and new ones are required when those sections are subdivided (section 3-116). A lost quarter corner on a line ending at the township boundary is reestablished "by proportionate measurement based upon the official record" (section 3-115).

Why it matters for mining claims

Placer mining claims located by legal subdivision follow quarter and quarter-quarter lines, and a mineral survey is tied to the nearest corner of the public land survey (Manual section 10-133), which may be a quarter corner. A quarter corner that was never set, was set 40 chains from one end rather than at the midpoint, or was restored after being lost will move the quarter lines and every aliquot part built on them.