Abstract Landslides and floods of lava and water tremendously affected the Columbia River during its long history of transecting the Cascade Volcanic Arc. This field trip touches on aspects of the resulting geology of the scenic Columbia River Gorge, including the river-blocking Bonneville landslide of ~550 years ago and the great late-Pleistocene Missoula floods. Not only did these events create great landscapes, but they inspired great geologists. Mid-nineteenth century observations of the Columbia River and Pacific Northwest by James Dwight Dana and John Strong Newberry helped germinate the “school of fluvial” erosion later expanded upon by the southwestern United States topographic and geologic surveys. Later work on features related to the Missoula floods framed the career of J Harlen Bretz in one of the great geologic controversies of the twentieth century.

Abstract Most of Oregon has been mapped as having low radon potential. Overall, elevated levels of indoor radon are found in only 4% of Oregon homes compared to 8% of homes nationally. Most maps show Portland, Oregon’s largest city, as having low to moderate potential for indoor radon. Using data collected by the Oregon Health Division’s Radiation Protection Services Section, we found Portland to have elevated radon values in 22% of homes. A radon potential map has been produced for 39 zip code regions of Portland based on the rank sums of maximum radon values, average indoor radon values, and the percentage of homes with radon values >4 pCi/1. Eight zip codes have high, 15 moderate, and 16 low radon potential. The maps were constructed by taking the indoor radon values from 1,135 homes, categorizing the data in terms of radon values, and plotting the points geographically by zip codes. Trends became obvious when geologic maps were compared to the areas of radon potential. Most of the high potential sites lie on highly permeable Missoula flood sediments. The data and map of radon potential were presented to the public through television and radio interviews and newspaper articles in June of 1994. The public, already familiar with the zip codes, could understand how to use the map. People in high to moderate categories were strongly encouraged to test their homes. A telephone number was given to receive free information on radon testing and mitigation.

Abstract The Lower Mississippi Valley is a 780-km lowland in the south-central United States extending from near Cairo, Illinois, south to the Gulf of Mexico (Fig. 1). Valley width varies from about 40 to 200 km, and flood-plain elevations range from about 84 m at the Mississippi-Ohio River confluence to sea level where the deltaic plain meets the Gulf of Mexico. The lower Mississippi is North America’s largest river. Its chief tributaries are the upper Mississippi, Missouri, Ohio, Arkansas, Red, and Ouachita Rivers. The drainage basin encompasses over 3,200,000 km 2 , and average discharge to the Gulf of Mexico is approximately 12, 000 m 3 /s, with a recorded maximum and minimum of 56, 000 and 5, 600 m 3 /s. The lower Mississippi Valley has developed since at least Cretaceous time in a terrain of igneous, metamorphic, and sedimentary rocks as old as Precambrian. The sediment delivered to the delta is chiefly silt and clay. Cycles of delta growth and deterioration have affected the amount of sediment delivered to the chenier plain west of the delta by longshore drift.