Chiwawa Mountain is located in the Cloudy Pass batholith, an intrusive formation that was formed approximately 20 million years ago, during the early Miocene.[3][6] During the Pleistocene period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured and shaped the landscape.[7] Remnants of the Lyman Glacier remain on the northeast slope of Chiwawa Mountain. Glaciation was most prevalent approximately 18,000 years ago, and most valleys were ice-free by 12,000 years ago.[3]Uplift and faulting in combination with glaciation have been the dominant processes which have created the tall peaks and deep valleys of the North Cascades area.
Subduction and tectonic activity in the area began during the late cretaceousperiod, about 90 million years ago. Extensive volcanic activity began to take place in the oligocene, about 35 million years ago.[8]Glacier Peak, a stratovolcano that is 10.0 mi (16.1 km) southwest of Chiwawa Mountain, began forming in the mid-Pleistocene.[3] Due to Glacier Peak's proximity to Chiwawa Mountain, volcanic ash is common in the area.
Climate
Chiwawa Mountain is located in the marine west coast climate zone of western North America.[3] Most weather fronts coming off the Pacific Ocean travel northeast toward the Cascade Mountains. As fronts approach the North Cascades, they are forced upward by the peaks of the Cascade Range (orographic lift), causing them to drop their moisture in the form of rain or snow onto the Cascades. As a result, the west side of the North Cascades experiences high precipitation, especially during the winter months in the form of snowfall.[3] Because of maritime influence, snow tends to be wet and heavy, resulting in high avalanche danger.[3] During winter months, weather is usually cloudy, but, due to high pressure systems over the Pacific Ocean that intensify during summer months, there is often little or no cloud cover during the summer.[3] Due to its temperate climate and proximity to the Pacific Ocean, areas west of the Cascade Crest very rarely experience temperatures below 0 °F (−18 °C) or above 80 °F (27 °C).[3]
