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, that examines the constitution, section by section, printing each section, then referring to the Journal (which is chronological) and citing contemporary newspaper articles and later secondary sources about the constitution.
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 here.
This site presents the Journal in two formats: an unedited PDF (made possible by William S. Hein Company, the publisher of the reprint) and a PDF with hyperlinks inserted so the researcher can easily go from a citation in the Journal to the material cited. (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.