The remote and sparsely-populated Trinity Alps are part of the Klamath Block of mountains. The resemblance between the Klamath Block and the northern Sierra Nevada is immediately apparent on observation even to a non-geologist. Geologists know that these mountains were connected to the Sierra at some point during the Mesozoic Era, but split off and moved 100 km/60 mi east. David Alt and Donald W. Hyndman, in "Roadside Geology of Northern and Central California," explain that they believe that the Klamath Block probably split off during the Jurassic Period. How a giant chunk of granite leaped so far from its point of origin remains a geologic mystery. But geologic mysteries make great places for exploration.