Ask Mr. Smarty Plants

The first part of your question is relatively easy to answer. You can find a list of native plants of Washington by doing a "Combination Search" in our Native Plant Database. You can find lists of native plants in the different counties of Washington on the Washington Native Plant Society website. You can also obtain lists of native plants in each of the counties of Washington by choosing "Advanced Search" on the USDA Plants Database
webpage.

There are a large number of characteristics you can choose to display in the lists from the USDA Plants Database. Unfortunately, these characteristics don't include "ability to absorb trace elements". Indeed, the ability of plants to absorb trace elements depends on many factors. As stated by K. M. Bali and J. N. Guerrero in Land Applications of Biosolids in the Imperial Valley (1996. Universtiy of California Cooperative Extension):

"The uptake of heavy metals and trace elements by plants depends on the concentration of theses (sic) elements in soil as well as on complex sets of other factors related to soil geochemistry.... The most important soil factors that influence plant uptake of elements are pH, clay content, soil texture, root depth, organic matter content and the presence of competitive ions (such as S for Se uptake). In addition, plant species vary in their ability to accumulate and tolerate trace elements and heavy metals."

So, I'm afraid we can't really answer that part of your question. Your best bet, I would think, is to search for relevant data on absorption of specific trace elements by a particular species of plant.