The Appalachian Trail consists of 2,168 miles of breathtakingly beautiful country. It extends from the top of Mt. Katahdin in Maine to the top of Springer Mountain in Georgia. The Trail passes through New Hampshire's White Mountains and Vermont's Green Mountains, the Berkshires, Catskills, and Poconos. Towards the southern end are the Appalachian Mountains, the Shenandoah Valley, and the Great Smokies. Hiking through these mountain ranges is very challenging. In fact, some say "brutal." To date, most people have taken about six months to hike the entire Trail -- if they have succeeded. In 2001, 2,375 hikers began, but only 389 finished.
"Hiking through these mountain ranges is very challenging." The active verb is "is". There is also a gerund, "hiking" which serves as the subject of the sentence. The subject clause is "Hiking through these mountain ranges", so even though "hiking" is a verb form, a gerund, it is not the verb in this sentence; it is part of the subject clause.
The rest of the passage contains other types of verb clauses, so you need to study those until you understand them.