This work on Marquam Hill area in Portland, a relatively undeveloped urban hillside area, is a pilot study in which environmental factors are evaluated quantitatively in order to delineate limitations on development. The study was undertaken at the request of and in cooperation with the City of Portland Planning Commission and with the State of Oregon Department of Geology and Mineral Industries. Factors considered include various aspects of the land, vegetation and attitudes of inhabitants. Findings are not intended to satisfy need for individual site studies by qualified experts but should show where that expertise is needed. Field data were collected on site by observations, borings, personal interviews and by geophysical surveys; laboratory tests were made on soil samples; studies were compiled of topographic maps and aerial photographs; and pertinent data from available previous works were incorporated. Data were integrated into a series of environmental factor maps including ground slope, bedrock and soil, bedrock structure, soil thickness, ground stability, hydrology, and vegetation. Land use constraints and environmental limitations were defined using u.s. Department of Agriculture, Soil Conservation Service, soil suitability and limitations criteria as a guide. Mapped geologic and environmental constraints were overlayed with the mapped soil criteria to identify areas by limitations. An interpretive map and chart show that most of the study area is moderately to severly limited for most land uses. Some small areas can be considered as slightly limited, but the majority of these are already developed. The constraints are so severe that most of the area should be left in open space. The major recommendation is that any development must be carefully controlled, utilizing stringent grading codes (such as Chapter 70 of the Uniform Building Code) and professional expertise to assure the safety and environmental compatibility of the site. It is suggested that planned unit development, in the form of clustered or low- to medium-rise structures would optimize design for natural conditions, siting locations, and residential density least affecting the surrounding, naturally vegetated, hazardous slopes.

Growing concern over earthquakes in the Pacific Northwest has prompted the mapping and location of near surface faults in the Portland area, Oregon. Visible evidence of faults is poor, requiring the use of geophysical methods to assist in mapping and defining structures in the basin. Gravity maps and models may help in addressing this problem.

The recent contributions of several investigators has indicated the Portland basin may be a pull-apart structure associated with wrench tectonism. Because of the large density contrast between sedimentary and volcanic units and because of their reasonably uniform and continuous nature, gravity survey methods can be used to identify covered structures with considerable success. The study utilized gravity modeling techniques to investigate the structure and genesis of the Portland basin's eastern margin.

Instrumental Neutron Activation Analysis (INAA) was used to identify geochemical groups in Boring Lava along the west side of the Tualatin Mountains, and in sediments of the Portland and Tualatin basins. Samples of Boring Lava were obtained from TriMet drill core collected during planning of the tunnel alignment for the Westside Light Rail line. Additional samples of Boring Lava were collected from outcrops along the west side of the Tualatin Mountains. Samples of sediment from the Tualatin and Portland basins were obtained from drill core collected during an Oregon Department of Geology and Mineral Industries (DOGAMI) Earthquake Hazards Mapping project. INAA of Boring Lava samples resulted in the identification of three geochemical groups. Additional data sets, including x-ray fluorescence geochemistry, magnetic polarity, and age dates, allowed for the distinction of three Boring Lava units. The Boring Lava of Barnes Road is a young, normal unit, the Boring Lava of Sylvan Hill is an older normal unit, and the Boring Lava of Cornell Mountain is the oldest, reversed unit. The surf ace distribution, identified using topography and outcrop geochemistry, is consistent with the subsurface distribution, identified using boring logs and core geochemistry. Volcanic vent locations are proposed at topographic highs within the identified surface distribution of the Boring Lava of Barnes Road. INAA of sediment samples resulted in the identification of seven groups: (1) Columbia River source sediments, (2) lower Troutdale Formation, (3) Reed Island ashes, (4) young Columbia River sediments, (5) highalumina basalt sediments, (6) episodic Cascadian volcanic sediments, and (7) Columbia River Basalt Group (CRBG) sediments. Only the CRBG sediments group was identified in the Tualatin basin, while all seven groups were identified in the Portland basin. This appears to demonstrate that the sediment packages in the two basins are different. Finally, each sediment group can be placed into one of three broad geochemical categories: Columbia River source sediments and lower Troutdale Formation represent a Columbia River or continental source; Reed Island ashes, young Columbia River sediments, high-alumina basalt sediments, and episodic Cascadian volcanic sediments represent a Cascadian or local source; and CRBG sediments represent residual soils or sediments overlying Columbia River basalt flows.

The state gravity maps of Oregon and Washington show a gravity high centered south of Portland, Oregon and a gravity low in the Tualatin Valley to the west disrupting the regional gravity gradient which is controlled by crustal thickening. Detailed gravity surveys done in the Portland area are consistent with the state gravity maps but show considerably more detail. Quantitative interpretation of this data has provided new information on the subsurface structure in this area; recent work has yielded corroborative evidence for a fault zone bounding the east side of the Portland Hills, and has indicated the presence of faults under the Portland Basin to the east which were previously unknown.