Aliquot Part

An aliquot part is a legal subdivision of a section made by dividing it into halves or quarters. The NE1/4 of a section is an aliquot part, and so is the SW1/4NE1/4, a quarter of a quarter.

BLM's Glossary of Surveying and Mapping Terms, as quoted in BLM's Specifications for Descriptions of Land (2017), defines an aliquot part as "an area that is a legal subdivision of a section by division into halves or fourths ad infinitum; except lots." Lots are the other kind of legal subdivision. They are numbered rather than described by fractions.

How a section is divided

The Specifications describe the steps:

• The section is split into quarter-sections "by running straight lines from the established quarter-section corners to the opposite corresponding quarter-section corners." These nominal 160-acre units are written NE1/4, NW1/4, SW1/4, and SE1/4.
• Each quarter-section is split the same way into quarter-quarter sections of nominally 40 acres, written, for example, SW1/4NE1/4.
• A quarter-quarter can be split again into nominal 10-acre units, written, for example, NW1/4SW1/4NE1/4.

BLM's Manual of Surveying Instructions (2009) explains that a regular section is "subdivided into regular 'aliquot parts,' based on midpoint protraction and intersections" (section 3-32). The quarter-quarter lines are not drawn on the official plat (section 3-105).

Smallest legal subdivision

Under the general land laws, the unit of administration is the quarter-quarter section of 40 acres or a lot. The Manual adds: "Under mining and reclamation laws, the smallest legal subdivision is the quarter-quarter-quarter section of 10 acres" (section 3-2). Placer mining claims that conform to the public land survey are described in these legal subdivisions (section 10-108).

The four-component limit

"In theory, aliquot parts can be divided ad infinitum," the Manual says, but the common practice is a four-component description (section 3-33). The Specifications make this a policy. A 2 1/2-acre unit written SE1/4NE1/4NE1/4SW1/4 is acceptable. A description with five or more components, such as W1/2SE1/4NE1/4SW1/4SE1/4, is not. When smaller parcels are needed, an official survey or supplemental plat assigns lot numbers instead.

Halves of halves

The Specifications warn against writing "W1/2W1/2" because such a description "is ambiguous and subject to more than one interpretation." The correct form lists the parts: W1/2NW1/4 and W1/2SW1/4. By government measurement, a half is determined by "equally divided or at proportionate linear measurement of opposing lines without consideration of the areas of the halves," unless a contrary intent is explicitly shown.

Why it matters in research

The same symbols in a different order describe different ground. SW1/4NE1/4 and NE1/4SW1/4 are two separate 40-acre parcels. Mining claim filings, BLM case records, and county documents that describe land by aliquot part have to be read exactly as written and checked against the official plat. Regular aliquot parts exist only where the section is regular; irregular sections carry lots in their place.