THE GEOLOGY OF MIRABEAU POINT PARK: AN UNDERGRADUATE SERVICE-LEARNING RESEARCH PROJECT

Mirabeau Point Park is located in the central portion of the Spokane valley, along the southwest bank of the Spokane River. Comprised of approximately 56 acres, the park is presently administered by the City of Spokane Valley. This project was a cooperative between the City of Spokane Valley and Spokane Community College as a service-learning opportunity for geology students.

Although the site is located within the heart of the urban Spokane Valley, this area has remained relatively undeveloped and offers a scenic rural forest setting. The park has numerous walking trails and abundant outcrop exposures, which ultimately make for an excellent field study site for both students and the public.

Mirabeau Point Park occurs in the southern part of the Spokane Dome of the Priest River metamorphic core complex (PRMC). The bedrock geology here is composed primarily of Newman Lake Gneiss, a Mesozoic-aged granitic orthogneiss. Extensive pegmatite veining occurs throughout the orthogneiss. In essence, the park is part of a larger bedrock “island” within the Spokane valley, surrounded by a thick sequence of Missoula flood deposits. Throughout the park, the Newman Lake Gneiss exhibits strong foliation, mineral lineation, and pervasive mylonitization. The mylonitization (blastomylonite) is characteristic of the upper part of the PRMC within the Spokane Dome mylonite zone. Bedrock knobs and adjacent gullies have a consistent NNE-trend suggesting possible structural control to topography. Scattered throughout the park are cobble to boulder-sized Missoula flood deposits and possible dropstones. Outcrops adjacent to the Spokane River exhibit various fluvial erosional features.

Mirabeau Point Park has numerous quality examples of basic and complex geology that are easily accessible to the public. This undergraduate service-learning research project was developed to create earth science awareness and education opportunities for the general public that utilize the park. Field studies and interpretations will allow for the development of informational displays, a guided walking tour, and potential lesson plans for K-12 field trips.