 A dormancy of about 4,000 years was broken around 2500 BCE with the start of the Smith Creek eruptive period, when eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles. An eruption in 1900 BCE was the largest known eruption from St. Helens during the Holocene epoch, judged by the volume of one of the tephra layers from that period. This eruptive period lasted until about 1600 BCE and left 18 inches (46 cm) deep deposits of material 50 miles (80 km) distant in what is now Mt. Rainier National Park. Trace deposits have been found as far northeast as Banff National Park in Alberta, and as far southeast as eastern Oregon. All told there may have been up to 2.5 cubic miles (10 km3) of material ejected in this cycle. Some 400 years of dormancy followed.
