Contour Lines: Reading Terrain
A contour line joins points of equal elevation, so a set of them turns a flat sheet of paper into a picture of the land's three-dimensional shape. Once you can read them, a topographic map tells you where the ground rises and falls, which way it tilts, and — most useful for a prospector — which way water runs across it. Because moving water is what sorts and carries gold, the contours that describe a hillside are also a map of where heavy metal tends to come to rest.
Contour Interval and Index Contours
The vertical distance between two adjacent contour lines is the contour interval. On a USGS topographic map this value is fixed for the whole sheet and printed in the margin, so every line you cross going uphill or downhill represents that same step in elevation. Intervals are chosen to suit the terrain and scale: a relatively flat area may use a 10-foot interval, while steep country may use 40, 80, or 100 feet or more, because tightly spaced lines would otherwise coalesce into an unreadable smear.
To keep counting manageable, every fifth contour is drawn as a heavier line called an index contour, and it is labeled with its elevation. The thinner lines between index contours are intermediate contours. To find the elevation of an unlabeled line, locate the nearest labeled index contour and count intermediate lines up or down, multiplying by the interval. Most USGS maps print contours in brown.
Reading the Shapes
The single most important pattern is spacing. Closely spaced contours mean a steep slope; widely spaced contours mean gentle, more level ground. Evenly spaced lines describe a uniform grade, while lines that bunch toward the bottom and spread toward the top describe a concave slope. Where contours appear to merge or touch, they are stacked one on top of another over a cliff or vertical face — and as a rule contour lines never cross, except at an overhanging cliff.
Closed, roughly concentric loops mark a hill or a ridge crest; the more rings, the higher it stands. A ridge shows as a series of nested U or V shapes whose closed ends point downhill, away from the high ground. A saddle — the low pass between two summits — appears as an hourglass pinch between two sets of closed contours, and is often the easiest place to cross a divide.
Valleys and drainages reveal themselves through the Rule of Vs. Where contours cross a stream or valley they bend into a V, and the point of that V always points upstream, toward higher ground. This lets you trace the direction of flow even on a dry map where no blue stream line is drawn. A depression — a basin with no outlet — is shown by closed contours carrying short tick marks, called hachures, that point downhill into the low spot, distinguishing it from a hill.
Why Terrain Shape Steers Water and Gold
Reading these features is not an academic exercise; it is how you predict where water concentrates, and water is the engine of placer deposition. Placer gold forms when weathering frees gold from a lode source and running water transports and sorts it, dropping the dense grains wherever the current slackens. The map's contours tell you where that slackening happens.
According to the USGS, gold in stream deposits is often concentrated on or near bedrock, and fine gold collects in pockets and depressions in sand and gravel bars where the current eases. The highest values tend to sit at the base of gravel, trapped by natural riffles in the streambed, by fractured or transverse bedrock, and above clay layers that block further downward migration — concentrations prospectors call pay streaks. Translated to contours: tight Vs mark the active drainages that gathered and carried the gold; the inside of a meander bend, where the valley widens and contours spread, is where velocity drops and heavy minerals settle; and a confluence, where two drainages join, doubles the catchment feeding a single channel. The shape of the land is the first filter for where to look.
In Lodester
Lodester's terrain and relief base maps — including USGS topographic layers — render these contours and shaded relief directly, so you can read interval, slope, ridges, and drainages without a paper quad sheet. Use the Rule of Vs on the topo layer to trace each drainage uphill to its source and downhill to its mouth, then follow that channel for the low-velocity spots placer gold favors: the insides of bends, confluences, and benches just above the active channel. Cross-reference promising drainages with the geology, hydrology, and prospectivity layers to see whether a likely source rock sits upstream, and check the BLM land and claims panel before working any ground. Every reading is anchored to WGS84 latitude/longitude, so a drainage you identify by its contour shape carries an exact coordinate you can mark, navigate to, or share.
This page is general reference information, not legal or financial advice. Always confirm land status and claim boundaries against official records before acting.