What is Trig Beacon?
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A triangulation station, also known as a triangulation pillar, trigonometrical station, trigonometrical point, trig station, trig beacon, or trig point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity.

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answer; gravity pulls glaciers down hill and as glaciers flow it pick up rocks and soil;