5.5 PLSS Sections, Townships, and Restoration

Public Land Survey System Essentials

The Public Land Survey System (PLSS) is the rectangular survey framework covering most of the U.S. west of the original colonies. FS questions ask you to interpret a description such as "the NE 1/4 of the SW 1/4 of Section 12, Township 3 North, Range 4 West," to compute aliquot acreage, or to explain why a section is not exactly 640 acres. The focus is conceptual and applied, not memorizing the entire BLM manual.

PLSS surveys are referenced to a principal meridian (a north-south line) and a baseline (an east-west line). A township is nominally a 6-mile by 6-mile block, located by township number north or south of the baseline and range number east or west of the meridian. Each township is divided into 36 sections, numbered in a boustrophedon ("ox-turning," serpentine) pattern: Section 1 sits in the NE corner, numbering runs west to Section 6, drops down and runs east 7–12, and continues alternating to Section 36 in the SE corner.

A normal section is 1 mile square and 640 acres, but real sections vary because of convergence, measurement limits, terrain, and original-survey adjustments. Nominal acreage is not treated as exact unless the facts support it.

Convergence, Correction Lines, and Aliquot Parts

Meridians converge toward the poles, so a perfect rectangular grid is impossible over large areas. To manage the distortion, guide meridians are run every 24 miles east and west of the principal meridian, and standard parallels (also called correction lines) every 24 miles north and south of the baseline. The original surveys began in the SE corner of each township and made all sections a full mile square except those along the north and west sides, where the accumulated excess or deficiency was thrown.

That is why the north and west tiers carry the odd dimensions and most government lots — irregular parcels used where aliquot division is impractical or where a section borders water or a state line.

Aliquot descriptions read from the smallest part outward to the section. "The SW 1/4 of the NE 1/4" is not the same parcel as "the NE 1/4 of the SW 1/4." Work inward: locate the section, then the first fraction, then the next. A quarter section is nominally 160 acres, a quarter-quarter 40 acres, and smaller aliquot parts follow by halving and quartering. Quarter corners (set at the midpoint of each section line) and the center-of-section corner control the interior subdivision.

Existent, Obliterated, and Lost Corners

PLSS retracement restores original corners and lines, not an idealized grid. The corner classification is the single most tested PLSS concept:

The rule is to exhaust the search for existent or obliterated evidence (bearing trees, accessories, fences, testimony) before declaring a corner lost. Only a truly lost corner is mathematically restored.

Closing Corners, Standard Corners, and Meander Corners

The convergence machinery produces several special corner types the exam may name. A standard corner is set on a standard parallel (correction line) when the line north of it is first run; a closing corner is set later where a survey line from the south closes onto that already-established parallel. A closing corner therefore may not fall exactly opposite the standard corner — that offset is expected, not an error, and you do not move the original closing corner to "fix" it. Meander corners are set where a section line intersects a meanderable body of water, anchoring the meander line that approximates the shore.

Recognizing these labels keeps you from forcing the grid into a perfect rectangle.

Fractional sections and government lots arise along the north and west township tiers and along meandered water. A government lot is identified by number (Lot 1, Lot 2) with an acreage stated on the plat, because no clean aliquot fraction fits. When a description calls a government lot, use the plat acreage and the meander/section lines, not a presumed 40- or 160-acre block.

Proportionate Measurement

Single proportionate measurement restores a lost corner that lies on a single line between two existent corners — the excess or deficiency along that line is distributed proportionally between the controlling corners (a "two-way" proportion). Double proportionate measurement restores a lost interior corner controlled by four corners: the north and south corners fix the latitudinal (north-south) position, and the east and west corners fix the longitudinal (east-west) position.

The FS exam is far more likely to ask which method applies, and to insist that original evidence controls over ideal geometry — never move an original corner just to make a perfect square or force a section to exactly 640 acres.