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They are notated by round blue circles with dashed lines inside of the circles. The lines will point in different directions to notate if the glaciers or snowfields are advancing or retreating.  Find a complete list of symbols on topographic maps at https://pubs.usgs.gov/gip/TopographicMapSymbols/topomapsymbols.pdf  It may be useful to bring a list of symbols with you when you use the map so you can refer to it as needed. Streams and rivers that are ongoing appear as solid blue waves on the map. Streams and rivers that are intermittent, where there is a break in their flow, have dashed lines or dots in the wave. Dams are notated on the map by two blue squares locked together. Buildings appear as small block boxes on the map. They may appear as solid black boxes or shaded boxes. Schools are notated by small black dots. Athletic fields appear as triangles or boxes with dashed lines. Other man-made objects like wells, tanks, and cemeteries are notated on the map using specific symbols. Find picnic areas by looking for red tables. Roadside rest areas appear as small black tables on the map.

Summary:
Look for a blue symbol for glaciers or snowfields. Identify the type of river or lake with blue wave symbols. Locate buildings and schools by finding black boxes. Check for campgrounds by looking for red tents.