What is the best way to establish an accurate elevation from USGS topographic maps for field surveying?

• A. Contour line
• B. Ridge line
• C. Benchmark
• D. Stream gauge

Answer: (C)

Establishing an accurate elevation relies on a fixed reference point that has a known, published elevation tied to a standard datum. A benchmark on USGS maps serves exactly this purpose: it marks a precise elevation value at a known location, so you can locate that point in the field and determine other elevations relative to it through leveling or height measurements. Contour lines only show relative elevation differences and require interpolation between lines, which introduces uncertainty for exact field elevations. A ridge line is simply a topographic feature, not a fixed elevation reference, and a stream gauge measures water surface level, not the ground surface elevation. Using a benchmark gives you a reliable vertical control point, enabling accurate elevation determinations in the field.