Biostratigraphic study of marine Cenozoic rocks of the Pacific Northwest began some 75 years ago, in part as a consequence of the discovery of petroleum in neighboring California during the late 1800s. It was preceded, however, by an almost equally long period of reconnaissance and early description that began during the middle 1800s. Paleontological study of the marine Cenozoic was initiated by T. A. Conrad’s descriptions of Oligocene and Miocene fossils from Oregon. The first biochronologies were developed by C. E. Weaver and, to a lesser extent, by Ralph Arnold and Harold Hannibal during the early 1900s. Their molluscan-based horizons and formations formed the principal means of age determination and correlation until the mid-1900s when the California-based benthic foraminiferal zonations were adapted to the Pacific Northwest Province by Weldon Rau. Recent development of worldwide planktonic microfossil zonations has created a renewed interest in biostratigraphic study of the Pacific Northwest in addition to a means of calibrating the benthic chronologies.

Grove Karl Gilbert (1843–1918) began his work in professional geology in 1869 as “local assistant” on the newly established Second Geological Survey of Ohio (the “Newberry Survey”). He worked without salary but received $50 per month for expenses. Gilbert investigated Williams, Fulton, and Lucas Counties, the three most northwestern counties adjacent to the Michigan State line. The area extended from Indiana on the west to Toledo at the western end of Lake Erie. His originality, analytical power, and clear verbal and graphic exposition, which were the distinguishing characteristics of his work throughout his career, are completely exhibited in this his earliest work, published in nine articles and reports from 1871 to 1874. Gilbert’s maps of glacial geology of Williams and Fulton Counties are noteworthy for their detail and accuracy. He was the first to discover and map the major end moraines of the Maumee basin, from east to west (youngest to oldest): the Defiance, Fort Wayne, and Wabash Moraines. Gilbert found that the drift sheets of the moraines were actually multiple and that the uppermost drift was draped over a core of older material, a concept not to be widely recognized until almost 50 years later! Gilbert discovered the continuity and mapped the beach ridges now called, from highest to lowest, Maumee, Whittlesey, and Warren. After distinguished work in the West from 1871 to 1881, Gilbert returned to the East and, among other projects, began to study the glacial geology of New York, especially Niagara Falls and the Lake Ontario raised beaches. In his classic study of the origin and retreat of Niagara Falls, he concluded that the Horseshoe Falls had retreated at the rate of 5 ± 1 ft/yr. Gilbert’s other work in the Ontario basin was on the uplifted shorelines of Lake Ontario, the character and amount of their later tilting, and the surface features and drainage channels of the Rochester region. He was impressed by the boulder pavements in the till and by the evidence of glacial and postglacial folding and faulting, on which he published several papers.