In North Cascades National Park, fire was used by Native Americans in the region near present-day Ross Lake to clear out brush, to ease foot travel, and possibly to flush animals out of the foliage. Evidence found in the patterns of tree growth as well as from tree ring analysis indicates human-caused fires were created for many hundreds of years. Similar evidence is found in the Stehekin Valley, where both smaller low intensity fires and larger fires are suggested by the growth patterns and burn scars in tree ring evidence. The low-intensity fires that were likely human induced were only found in the easternmost regions of the park. In the subalpine regions such as the Thunder Creek area, the studies concluded fire occurs at frequencies ranging from 30 years to 400 years.