The Tumwater Historic District is of exceptional historical significance as the site of the first permanent American settlement in the Puget Sound basin. Established in 1845 as "New Market" by a pioneer party led by Michael T. Simmons and George Bush-a notable free Black pioneer who played a vital role in the settlement's success-the district represents the terminus of the Oregon Trail's northern branch. Strategically situated at the falls of the Deschutes River, the settlement quickly harnessed the river's immense water power to operate the region's earliest American-owned gristmills and sawmills. This industrial activity broke the Hudson's Bay Company's monopoly on lumber and grain in the Pacific Northwest, paving the way for rapid American colonization and the eventual creation of the Washington Territory.

In the late 19th century, the district's industrial identity shifted from milling to brewing, initiated by Leopold Schmidt's founding of the Capital Brewing Company (later the Olympic Brewing Company) in 1896. Capitalizing on the area's pure artesian springs, the brewery became one of the largest and most technologically advanced operations in the West, defining the local economy for generations. Today, the historic district retains an array of significant architectural resources that chronicle its evolution from a pioneer outpost to an industrial powerhouse. Key landmarks include the iconic 1906 brick brewhouse, the elegant 1904 Schmidt House, the 1854 Crosby House (one of the oldest surviving frame homes in the state), and the Henderson House, all of which collectively preserve the rich social, industrial, and architectural heritage of western Washington.

The Washington State Capitol Historic District, listed on the National Register of Historic Places in 1979, serves as the grand civic and architectural centerpiece of Washington's state government in Olympia. Conceived during the height of the "City Beautiful" movement in the early 20th century, the campus represents a masterful integration of monumental Beaux-Arts architecture and picturesque landscape design. The overall group plan was designed in 1911 by the prominent New York architectural firm Wilder & White, who envisioned a formal, acropolis-like setting on a forested bluff overlooking Capitol Lake, the Puget Sound, and the Olympic Mountains. This monumental vision was further enhanced by a comprehensive landscape plan executed by the world-renowned Olmsted Brothers, creating a park-like environment of sweeping lawns, formal plazas, and native plantings that symbolizes the growth, stability, and democratic ideals of the state.

At the heart of the historic district stands the majestic Legislative Building, completed in 1928, which features a soaring 287-foot masonry dome that is one of the tallest of its kind in the world. This monumental anchor is flanked by a symmetrical arrangement of classical sandstone edifices, including the Temple of Justice, the Insurance Building, and the Cherberg and O'Brien buildings, all unified by their Neoclassical styling and use of locally quarried Wilkeson sandstone. The district also encompasses the elegant, Georgian Revival-style Executive Mansion (1908), the state's oldest continuously occupied official residence, alongside a collection of notable commemorative memorials and public art. As the seat of Washington's executive, legislative, and judicial branches, the district is of paramount historical significance for its outstanding architectural cohesion, its landscape artistry, and its role as the enduring stage for the state's political and social history.