Understanding how to read a topo map is very important to finding the claim areas listed in the mining guide and is an invaluable tool for understanding how gold may have moved on the claim sites, allowing you to prospect more efficiently and get the gold quicker!
The U.S. Geological Survey (USGS) began mapping and creating topographic (topo) maps in 1879 to better understand and catalog public lands. The first maps were plotted by cartographers (map makers) finding high spots and using sighting tools like sextons to approximate distance and elevation to draw their maps. These maps were the most accurate for the time but were best thought of as “mostly accurate”. Over the years, topo maps became more accurate with aerial photography and now with satellite imaging, topo maps are more accurate than at any time in the past and can be depended on for all forms of locating surface features.
What is a topographic map?
Topo maps have been the best described as offering the user a three-dimensional view on a two-dimensional sheet. Topo maps show contours, elevations, mountains, valleys, bodies of water and much more.
For a prospector, a topo offers features that are very important in your quest for gold. By studying a topo, you will locate old and current roads, trails and town sites, water flow areas along with slopes, mountains, valleys and on many maps, mines are shown. All of these are crucial if you are looking for an area that has produced gold in the past and with practice you can create a best guess as to how the material was worked before visiting the site or deciding to pass.
Here is an example of using a topo to decide what equipment to bring to an area. Looking at a topo you find an area that has a number of mines shown on the map. The terrain is somewhat steep and there are a number of trails leading into the area and out to major roads. There are no water ways such as streams or rivers in the area and the closest ones do not have roads leading to them from the mine sites. The area also does not show much flat terrain around the mines themselves. This area on the map tells us volumes about the mines and what type of work was being done. Because of the slope steepness we can guess that the mines were hard rock or lode mines. There are a number of trails and very little flat terrain and no available water. This tells that the material was most likely not processed on site due to the lack of flat space and water. The roads lead directly to major roads which tells that the material mined was no doubt taken from the site for processing. Now, if in researching the area you find that the mines in the area were gold mines then the assumption would be that the ore was most likely higher grade ore that made it profitable to remove all of the material and haul it to a processer. In this area the likelihood of finding a good amount of gold with a drywasher or recirculating water unit may not be the best technique for recovery.
The first process to becoming proficient in reading a topo is learning to understand the lines that cover the map area. The lines on a topo map are the indicators for contours, roads, property sections. Solid, dashed, or both and in different colors all indicate different information. You will also find curved lines to indicate terrain changes and other features such as elevation change where a hill will have a larger circular line at the bottom to show the base of the hill.
There are also a number of symbols on a map in a legend describing the symbols. You can also purchase a mapping book that includes all of the information that is included on a map. While learning what all of this information is, that small investment in the publication is well worth the cost. You will find that you will use this often, especially in looking over maps for a new area where there are unfamiliar symbols. Some of the symbols you will find on a map are for quickly knowing boundaries, buildings, contours, survey monuments, mines and caves, railroads, waterways, roads and related features, power and phone lines to name a few.
Contour lines are the most recognized feature on a topo. The lines show equal elevation and if you were to drive or walk a contour line for miles and miles, you would never increase your elevation. Contour lines also show the elevation along with the shape of the land and its features like steep mountains, gradual hills and the steepness of banks going into streams and river. All of this is excellent information to have before heading into the field to prospect. Plus knowing the terrain flatness or slope again tells a great deal of information on how gold would be moving in an area.
Understanding the lines on a map is relatively simple and can be mastered with little practice. Topo maps only include lines for set elevations. The lines are evenly spaced creating the contour interval. To make map reading easier, maps use different intervals depending on the topography. If the land has a sharp rise or drop like a mountain or gorge, the map may show the contour interval every 60 to 100 feet to show the steepness. This makes it much easier to see the rise of the mountain or the drop of a valley. As all maps vary, it is always good to look in the maps margin area. This is where the USGS list the contour interval for the map being used.
The lines however offer little information unless they include base information. On a topo map every 5th contour line is called the index line and it will be a thicker and darker brown line. There will be breaks in the line that include the elevation information. This will give you the base line of the steepness of the terrain. One example of index lines is if you see a line that in the break reads 500 then it is known that the elevation of this line is 500 feet. If the fifth line from there reads 600 then you will know that the four lines would indicate that there is a 20 foot increase in elevation for each line making this a steep slope. Conversely, if looking at a map and the four lines between the index lines are spaced far apart, there is little raise in elevation and it is relatively flat land.
On a topo map every 5th contour line is called the index line and it will be a thicker and darker line that is brown.
Looking at the map on the right of the area around Stanton, Arizona you can easily see elevation changes in the index lines from the desert floor to the top of the mountain to the north on the map.
The next part in reading a topo is understanding scale. Maps are plotted on a ratio scale, meaning one measurement on the map equals a measurement of actual distance on the map.
On a USGS topo, the standard first unit of measurement is one inch and the second unit is ground distance. If at the bottom of your topo the scale is listed as 1:24,000 it simply means that one inch on the map is equal to 24,000 inches or 2000 feet of distance. There are a number of different scales and it is suggested that when buying maps that you use only one scale if possible. This will help in plotting areas that may be on more than one map sheet.
As an interesting point of trivia, the USGS topo map catalog has over 57,000 1:24,000 maps to cover the 48 contiguous United States and Hawaii.
These are the three most important TOPO Mapping symbols to a prospector:
Prospect - Where they Prospected
ADIT - Where a shaft was opened
Tunnel - Where they worked.
Seeing these symbols on a Topo will give you a good idea where to look in the peripheral Placer areas to get on the gold.
By using a Topo Map, areas that I described in the Claim Review below start to stand out. Notice the X X X to the south of the claim? Those are mine sites and I have found others on the claim that are not registered and not on the Topo. Most importantly I used this info for elevation which helped me a great deal on locating my spots on the claim.
Before you spend a lot of time jumping into the water channels prospect the old benches, fans and depressions. Especially those that are showing a lot of red iron staining or compacted gravels above the water channels.
Some of these areas are less than a few feet across and can be easily missed. I generally start out here with a gold pan, (dry panning) and a detector. I've found a few nice nuggets in these areas then following up with a drywasher.
When I'm drywashing well out of the water channels the gold is somewhat coarse and small. Of course the closer I get to the water channels the finer and the more smooth the gold becomes with a great deal of it being flood gold that I recover on the flood benches.
Kevin Hoagland is the Executive Director of Development at the Gold Prospectors Association of America and the Lost Dutchman's Association of America. He can be reached at firstname.lastname@example.org