The maps in this folder are survey plats, drawn in the 1850s to1870s. After California became a state, the General Land Office hired surveyors to survey the public lands in the state, with the task broken down by 36 square mile areas called townships. As part of the job of surveying a township, the surveyor drew a plat, which was intended to facilitate relocation of witness posts and survey stakes. Besides the section lines and features along the section lines, the plats sometimes show other features of the landscape, including vegetation, streams, houses, fences and fields, and some topographic information.
Because the initial surveys were done shortly after European settlement in the Mattole Valley, these plats are of interest for natural as well as cultural features. For example, the notations on vegetation show that chaparral was common in the area, presumably because burning by Native Americans promoted that type of vegetation. However, this evidence should be interpreted with caution, since describing the vegetation was incidental to the purpose of the surveys. Notes of trees or other features on the section lines are specific, but notations such as “Rough Mountain Land Covered with Chaparral” are generalizations that probably describe the dominant vegetation, and most likely there was forest on the north slopes and in the draws in these areas, as well as areas of grassland or oak woodland.
Townships are divided into sections of one square mile. Sometimes, quarter sections were surveyed as well. Property descriptions in rural areas typically refer to the sections lines or section quarters. Townships are referenced to east-west and north-south lines called base lines and meridians, in units of six miles called ranges and townships. In Humboldt County, these lines run through a point on Mt. Pierce. For example, Petrolia is in Township 2 South, Range 2 East, Humboldt meridian and base line. For most of the state, including parts of the Mattole basin in Mendocino County, the mapping is referenced to the Diablo Meridian.
Plat 1N 2W Bear River
Plat 1N 3W Cape Mendocino
Plat 1S 2W Lower North Fork
Plat 1S 3W 7 Mile
Plat 2S 1E Rainbow Ridge
Plat 2S 1W McGinnis Creek
Plat 2S 2W Petrolia
Plat 3S 1W Squaw Creek
Plat 3S 2W Lost Coast
To allow faster downloading, we have reduced the files from about ten megabytes to about two, and added geographical notations, but those wanting finer resolution can download the larger files from www.glorecords.blm.gov in three formats: pdf, sid, and jpg (or google “general land office records” and select “Home – BLM GLO Records”). The sid files are also about ten megabytes, but viewing them requires a special viewer, downloadable free from Lizard Tech. The jpg files are very large, over 100 megabytes.
To find the plat for your area, you need to enter the numbers and direction of the township and range, which you can find in the margin of the relevant USGS topographic map.Select the plat image button for the oldest plat, scroll down and select “basic viewer,” and the plat should appear. There are buttons for downloading the plat at the lower right corner of the screen.