Boulder taxed itself to buy open space and drew a 'blue line' on the map

The open hills around Boulder, the ones that keep the mountain backdrop free of houses, did not stay empty by luck. The city made deliberate, durable choices to protect them.

Two of those choices stand out. First, in 1959 a charter amendment created what people call the “blue line,” a boundary on the lower mountain slopes above which the city would not extend water service. Without city water, dense building uphill became impractical, which helped keep the backdrop open. Second, in 1967 Boulder voters approved a dedicated sales tax to buy, manage, and maintain open space. The City of Boulder describes this as an early example of a community taxing itself specifically for that purpose, and the program has acquired hundreds of properties since.

For a newcomer, this history explains a lot. It is why so much green land rings the city, why that land is actively managed with rules and trailheads, and why a small slice of what you spend in Boulder goes toward conservation. It also helps explain home prices and where building can and cannot happen.

Tax rates and program details change over time, so this note points to the structure, not a current number. The City of Boulder’s open space and sales-tax pages explain how the dedicated tax works and how the land is protected.