This word describes things that belong to geology: the rocks, soil, and other materials that make up the Earth, and the way they have changed since the Earth was formed. A geological map does not show roads and cities first; it shows what kind of rock lies under your feet, and how old it is. A geological survey means people going out to study the ground itself. A geological timescale is not in years you can feel — it is in millions of years. So the adjective does not mean “the study” by itself; it means “of that study / of those rocks and that long change.” Though actually, English speakers also stretch it as a joke. “I haven't cleaned this in geological time” means “for a ridiculously long time.” That use is playful. In school and science it stays close to rocks and Earth history. Do not use it when you mean geographic (about places and maps). A geographic border is on a map; a geological fault is a crack in the rock.