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).
Beverly Paulik Rosenow, The Journal of the Washington State Constitutional Convention, 1889, with Analytical Index by Quentin Shipley Smith (1999 reprint).