An essential tool for researchers is The Journal of the Washington State Constitutional Convention, 1889, edited by Beverly Paulik Rosenow in 1962 (reprinted in 1999). This volume includes an analytical index prepared by Quentin Shipley Smith examining the constitution section-by-section, with references to the Journal (organized chronologically) and citations to contemporary newspaper articles and later secondary sources about the constitution (pp. 491-885).
Rosenow's book also includes a section with biographical sketches of the delegates to the convention (pp. 465-90). For convenience, a PDF of just these pages is available here.
This site presents the Journal in two formats: (1) an unedited PDF (made possible by William S. Hein Company, the publisher of the reprint), and (2) a PDF with hyperlinks inserted so researchers can easily go from citations in the Journal to the materials cited.
Please note that the links lead to the source, but not to the specific reference within the source. For example, if the analytical index cites "Cal., Const. (1879), Art. 6, sec. 2," the link is to the California Constitution of 1879; the researcher will then need to go to Art. 6, sec. 2. When the analytical index cites a newspaper, the link goes to a list, by date and title, of articles in that paper