3.19
Cumulative Effects
Cumulative effects refer to the impacts from the CRC project when
added to the impacts from other past, present, and reasonably foreseeable
future actions. Cumulative effects can result from individually minor but
collectively substantial actions that take place over a period of time.
Input from resource agencies, Tribes, and the public helped define the
scope and scale of the cumulative effects analysis.
To address cumulative effects, the project team established a time-frame
of reference for evaluating how past actions have shaped existing
conditions, and how future actions might further change them. For the
built environment, the “past” runs from 1960 (prior to the opening of I-5)
to the present day. For the natural environment, an earlier base year is
evaluated to capture a longer history of the effects of development on
natural resources in the area. To determine base thresholds the cultural
environment team solicited input from the Cultural Resources/Section
4(f) Workgroup, which is composed of local and state agency
representatives, the Washington Department of Archaeology and Historic
Preservation (DAHP), and the Oregon State Historic Preservation Office
(SHPO).
Past Actions
Native Americans have occupied or traveled through the CRC project
area for thousands of years. Those activities had little effect on current
environmental conditions in the CRC project area. In the 1800s
European-American settlement began and the Portland and Vancouver
area population began to increase dramatically. The following key
historic events provide a basis for analysis of past actions that have
helped shape current environmental conditions:
Pre-1800s – Native American paths along Siskiyou Trail on what is
now the I-5 Corridor connected tribes from the Pacific Northwest to
California’s Central Valley.
1810 to 1850 – Settlement of Fort Vancouver and the Hudson Bay
Company. Commercial fur trapping on the Columbia and associated
waterways. Fur trappers from the Hudson Bay Company operating
out of Fort Vancouver adopted the Siskiyou Trail as a major
transport corridor between the Northern Oregon Territory and
California.
1846 – Ferry service across the Columbia between Vancouver and
Portland was established and offered intermittently by various
operators.
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1890s – Trolley line system in Portland and Vancouver encouraged
greater urbanization and development of neighborhoods east of the
Willamette in Oregon, and north to Fourth Plain Boulevard in
Vancouver.
1905 – Pearson Airfield became a dirigible landing area. It was
officially dedicated as Pearson Airfield in 1925. The automobile was
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