For the seasoned prospector reading topo maps is second nature, but for the beginner it may not be so easy. There are subtle things on a topo map that even an intermediate user may not fully understand or may not have even noticed before. Today we will cover the basics, but also get into some of the more fun technical details and tricks.
First lets look at a few different common map sizes used by prospectors.
This is a 1:250,000 scale or 250K map. Ever inch on this map represents five miles on the ground. These maps are useful for getting a general overview of an area or mountain range.
This is a 1:100,000 scale or 100K map. Every inch on this map represents one mile on the ground. These maps are VERY USEFUL for figuring out general land ownership and also for determining section, township, and range for use in staking claims and the BLM LR2000. We will discuss this further later in the article.
This is a 1:24,000 scale or 24K map. This is the most detailed map you will generally find on any area. These maps are very useful for finding specific features such as mine shafts or trails. They are also commonly used for mapping out mine claims to be submitted to the county or BLM office. These are the maps we usually load onto our GPS for use in the field. You can see the contour lines very well on 24k maps, these lines indicate the elevation of the terrain. The closer these lines are together the more drastic the elevation change. On 24K maps keep a close eye out for adit symbols, they are shaped like an elongated Y with the stem of the Y indicating the direction of the drift. Sometimes they get lost in the contour lines are are difficult to spot.
Now that we have covered the general topographical map sizes lets take a look at something we use very often in the mining industry.
Understanding section, township, and range.
In our modern world of GPS and Google Maps it can be somewhat difficult to get the hang of the Public Land Survey (PLS) system. This system has been around since the 1800’s in the United States and isn’t likely to be changing anytime soon. With this guide and a little practice you should have it down in no time.
This diagram illustrates how the PLS system works. You can see that range runs across the top of the map (East-West) and township runs up and down (North-South). Inside each of these township and range blocks are 36 one mile square areas called sections. Every section block of 36 starts with section #1 in the upper NE corner and ends with section #36 in the bottom SE corner. On 24K maps these sections are usually all labeled, in 100K and bigger maps you generally have to count them out as they only label the four corners (section #1, #6, #31, and #36).
To summarize with an example I am going to pretend I have a block of claims covering section 26. The PLS description for those claims would be township 27 south, range 12 West, section #26.
Now that we understand the PLS system of sections, townships and ranges, lets take a moment to look at determining general land ownership on a 100K map.
Determining land ownership on a 100K map.
As a prospector knowing the land status of any area I am working in is very important. 100K maps are very useful for this information, but keep in mind it may be out of date so be sure to check with the county before filing claims. In the map above this land status legend you can see that most of T27S and R12W is BLM land with the exception of sections 2,16,32, and 36 which are state land. White areas are private land, in mining areas they usually indicate patented claims.
Tips and tricks.
- When you are using a compass in the field you can get magnetic declination information from almost all topo maps.
- Remember that the features shown on a 24K map are usually drawn at the discretion of the cartographer. Sometimes prospects will show up as mines and sometimes large mines are only shown as prospects. Some mines and shafts aren’t on the maps at all. If a mine has a name on the map that is not always a good indicator of size or importance. Sometimes the biggest mines in a region will not be named on 24K maps while smaller mines are.
- Newer maps aren’t always the best for detail. Sometimes key features or historic information that may be useful to a prospector will disappear from newer maps. Always study all the available maps of a region to get the best feel for the area.
- Road conditions are also at the discretion of the cartographer and the whims of erosion. What is shown as a maintained road on an old map may only be a goat trail now. Four wheel drive trails may have been graded into 2 wheel drive improved surfaces, or they may be gone altogether. Sometimes an area on an older maps shows no trails, but is littered with them when you get there. Always double check your information when planning driving or off-road routes. Google Earth is a great way to take a look at current road conditions in an area. If a road looks overgrown and washed out it likely is.
If you have any questions, comments, or tips we should add, feel free to comment below.
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