Over what period of time would you expect to see large changes in mountains, canyons, and similar features of the earth?

If you've ever looked at the formation from Earth and look at the changes over millions of years you've seen differences. These differences are from weathering (snow, rain, ice) and erosion (small rocks). If you were to take a mountain about 1,000 feet tall, over let's say 100 years, it's going to change because of these factors.