Which AVA is shared between Washington and Oregon?

The Columbia Gorge AVA is indeed the correct answer, as it is one of the few American Viticultural Areas that spans two states—Washington and Oregon. This unique geographic characteristic allows it to enjoy a diverse climate and soil types, which benefit grape growing in both regions. The Columbia Gorge is known for its varying elevations and microclimates, which contribute to a wide array of wine varietals being produced, including both red and white wines. The ability of this AVA to utilize the river gorge's effects on temperature and precipitation is a key factor in its viticulture success.

In contrast, the other options are confined to a single state. Red Mountain and Horse Heaven Hills AVAs are entirely located in Washington, while the Yakima Valley also exists solely within Washington. This delineation highlights the special nature of the Columbia Gorge AVA as a cross-state region that showcases a broader range of wine production possibilities due to the combined climatic influences of both Oregon and Washington.