You can find lots of good sources at a Library (School or public).
An encyclopedia, not wikipedia, will usually be at either, look up geology, and look through how rifts, mesas, mountains, and other physical features are formed, and related.
The Library will also have lots of books about the topic. You can look them up in the library catalog. Search for books on Geology, or specific physical features e.g. mountains, plateaus, oceans, etc. to find more specific information.
Also look up Discovery.com, and NOVA on PBS.org. These websites have links to reliable information about the topic and videos that illustrate the geological processes that form most land features.