Figure 3. Thick tephra sequence about 6 km northeast of the center of Mount St. Helens along USFS Road 99. Outcrop is about 6 m high. All tephra deposits exposed here were erupted during the past 13,000 years. Layers Yn, Wn, and T are the most conspicuous tephras northeast of the volcano. Layers Yn and Wn are also two of the largest volume eruptions known of the past 13,000 years. Layer Yn thins noticeably from the middle of the outcrop to the left; only a small part of the difference evident is from scraping of the outcrop. Layer Wn, in contrast, thickens from the middle of the outcrop to the left. Photograph taken in 1965.