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Map Basics

Protracted Blocks (PB)

Why is there a "section" labeled PB43 on my map where I expected a section number?

 That PB stands for 'Protracted Block', which is an unsurveyed area (of uncertain acreage) of which parts of, but not the entire, boundary has been surveyed.  These ‘PBs’ will be found most often in areas with complete or partial  section surveys, such as in mining districts, areas with private inholdings or along Federal land boundaries. 

Some background:  The Public Land Survey System (PLSS) is the method by which public land in the United States is identified, established, and described.  The Bureau of Land Management is responsible for the PLSS.  In 1993, the BLM issued a manual that allows for the definition of unsurveyed areas in the lower 48 states and provides a stabilized protracted land net which helps to simplify the issuing of leases and identifying withdrawals on unsurveyed Federal Lands.

A protracted block is identified by its unique numbering system. The lowest protracted block number will be PB37 and it will be sequentially numbered, identifying each parcel that abuts a previously surveyed area. 

Map users should be aware of this difference in Section numbering from the standard 1-36. Until all users are aware of this change there may be confusion in communicating location based on the protraction block numbering.

Forest Visitor Maps and new SEQs (Single Edition Quads, or 7.5-minute topographical maps) now use the PB system. Only fully surveyed sections or completely unsurveyed sections will maintain the section numbers.

Why can’t I just continue to use the old section number?

In short, the old section number is no longer the official identification number for that particular piece of land until the section is completely surveyed and accepted by the BLM.  However, it remains important to understand the Township and Range system with the 1-36 section overlay and be able to communicate your location with the section number if needed, as not everyone understands Protraction Blocks, and certain base maps available for GPS and even for sale may not have accurate PB information.

Graphic showing a section that has been divided into protracted blocks, according to the PLSS
This graphic is an example of a section (1x1 mile or 640 acres, approximately) that was previously designated Section 23.  A portion of the interior of the section and portions of the boundary have been surveyed, and the area between the surveyed lines and unsurveyed lines been given PB designations.  In a given Township grid of 36 sections, the numbering for the PBs will start at PB37.  In this case, they are given the numbers PB43, PB44, and PB45 (other sections in the Township have PBs 37-42) .  PB45 is a Federal land withdrawal parcel, unsurveyed, but “protracted” and therefore distinct from PB44, which is Federal land in the public domain.