Portland Region Study Area

The study area consists of all or part of 25 counties in Oregon and Washington. However, since population data is available on a county basis, the following discussion is for the 20 counties shown in figure 1. This county-based study region contains all of the major population centers included within the rectangular study region used for mapping purposes.

Table 1 lists census data for each of the 20 counties, and figure 2 shows the total population for the entire 20 county region. Settlement in the region began in earnest in the mid-1800s with the availability of free land grants. It grew quickly in the 1850s and 1860s during the gold rushes in California, Oregon, and Idaho, because Portland became a center of trade for outfitting the miners. Another spurt occurred right after 1900 because of the Alaska gold rush. The 1940s saw a huge increase in industrial growth, particularly shipbuilding and war needs factories, which resulted in a population boom.

Figure 3 shows the population growth in each of the counties individually. Multnomah county in Oregon has seen by far the highest growth rates and highest populations; it is the county which includes Portland. Five other counties have experienced high growth rates since the 1940s, primarily the counties which include or surround the largest cities, such as Portland (Washington and Clackamas counties), Vancouver, WA (Clark county), Salem (Marion county), and Eugene (Lane county). Figure 4 shows the remaining 14 counties in more detail, which all have 1990 populations less than 100,000, and show slower growth rates. However they exhibit the same general trends of growth spurts after 1900 and 1940, and the population is driven by the presence or absence of a major urban center. The least populated counties are those along the coast and coastal range (Tillamook, Pacific, Wahkiakum), or in the Cascade mountains (Skamania, Hood River).