Here's a real-world scenario: you look at a BLM claim block on a map. It covers what appears to be a full 160-acre quarter section — a solid red rectangle on the screen. But you know that placer claims are limited to 20 acres. So either the map is wrong, or there are multiple claims stacked on the same 160-acre block, each covering a different 20-acre piece.
The PLSS_DESC field in BLM's MLRS is the key to understanding exactly which 20-acre slice each claim covers. If you can read aliquot notation, you can look at a cluster of claims and immediately know how much is actually open.
Think of a 640-acre section as a square. Divide it into quarters (N, S, E, W directions give you NE, NW, SE, SW). Each quarter is 160 acres. Now divide each quarter into quarters again — you get 16 cells of 40 acres each. Cut each 40-acre cell in half (north or south half), and you have 32 cells of 20 acres each. Those 20-acre cells are the standard aliquot used for individual placer claim locations.
The PLSS notation for each cell builds from the smallest subdivision outward. Reading the notation right-to-left takes you from the largest subdivision to the smallest piece.
| Notation | Reading | Acres |
|---|---|---|
| NE | Northeast quarter of the section | 160 |
| NWNE | Northwest quarter of the northeast quarter | 40 |
| N2NWNE | North half of the northwest quarter of the northeast quarter | 20 |
| S2NWNE | South half of the northwest quarter of the northeast quarter | 20 |
| E2 | East half of the section | 320 |
| N2SW | North half of the southwest quarter | 80 |
| SESW | Southeast quarter of the southwest quarter | 40 |
When BLM renders claim polygons on a map at the section level (160 acres), it often draws the full quarter-section rectangle even when the PLSS_DESC says the claim is only 20 acres. The map is drawing the bounding box of the legal description, not the precise aliquot footprint.
This is why you can see a solid-red 160-acre block on a BLM map and still find open 20-acre parcels inside it. The block represents a section with some claimed cells — but the unclaimed cells are still available for location. You have to parse the PLSS_DESC of each claim in the block to figure out which cells are taken and which are open.
You find a claim record with PLSS_DESC = "N2NWNE" in Section 14, Township 7 North, Range 3 East. Reading right-to-left: start at the whole section, take the NE quarter (160 acres), subdivide that into the NW quarter (40 acres), then take the north half (20 acres). You've arrived at a 20-acre parcel in the northern interior of the section's northeast corner.
The south half of the same 40-acre cell — "S2NWNE" — is a separate 20-acre parcel that could be open for location. So could the NE of the NW ("NENW"), the NW of the NW ("NWNW"), and the other 28 aliquot cells in the section.
When you drop a GPS stake pin in AuthoriProspector, the app reads the PLSS parcel data for that coordinate and returns the aliquot notation — down to the 20-acre cell. The Auto-Square feature then uses that notation to pre-populate the legal land description field in your Notice of Location PDF. No need to manually compute which aliquot your pin falls in.
AuthoriProspector overlays live BLM claims, 20-acre aliquot precision, USGS historic mine markers, and no-go zones on a single map. Tap any block to see who owns it — then stake and file from the field.
Map Open Aliquots on AuthoriProspector →