There are many reasons to support a federal bill that would create a Santa Cruz Valley National Heritage Area. The most compelling rests on the belief that our population and urban growth are increasing so rapidly that ties to the natural and social history of this region will become invisible if we don't do something to preserve them.

Reps. Raúl Grijalva and Gabrielle Giffords, who represent Southern Arizona, on Tuesday unveiled the bill that would designate approximately 3,300 square miles of the Santa Cruz River watershed as a heritage area. This isn't the whole watershed but the most populous portion, extending from Nogales in the south to Marana in the north, from Green Valley in the west to Elgin in the east.

The natural course of the river — which is a dry ditch most of the year — extends from its high point at the Arizona-Sonora border to its low point near the confluence of the Gila River south of the Phoenix area. The proposed heritage area is much smaller than that.

Designation as a national heritage area doesn't mean the use of private property is restricted, that livestock grazing or farming are involuntarily curtailed, or that the public will be kept out of federally managed lands.

It means that a modest amount of federal money becomes available in the region for education and other projects that enhance public awareness of the area's history and its cultural resources.

The term "cultural resources" is academic shorthand for those ingredients in our physical landscape that connect us to the people who lived here before us, as well as to our more recent history. It includes such diverse ingredients as the evocative remains of the 250-year-old Tumacácori Mission, five miles south of Tubac, and the Titan Missile Museum, an artifact of the Cold War, at Sahuarita.

A wide range of organizations representing businesses, historical groups, governments and agriculture are supporting the push for creation of a national heritage area in the Santa Cruz Valley (which includes Tucson).

Some of the support is based on the economic value that may come as an extension of capitalizing on the area's history and natural beauty. Small grants may become available, for example, to support the marketing of locally grown foods and native crafts, or to help a writer working on a new book about the area.

There are 22 National Heritage Areas throughout the United States. In 2006, they were supported by $13.3 million in federal funds. Yuma Crossing is the only National Heritage Area in Arizona. It's the point at which various expeditions traversed the Colorado River in the days before it was tamed by a series of dams.

The Santa Cruz Valley National Heritage area would dovetail nicely with development of the Tucson Origins Park. Groundbreaking for that project on the west side of the Santa Cruz River, south of West Congress Street, is scheduled for early June. It will include a re-creation of the San Augustin Convento, or mission, at the base of "A" Mountain.

Despite the rapid growth of our area, Southern Arizona remains unique in that it has not yet been completely swallowed by the rampant urbanization we see in metropolitan Phoenix and Las Vegas.

Visitors find it engaging to travel in a part of the country that continues to bear palpable evidence of three cultures — the indigenous O'odham and their ancestors, the missionaries and Spanish explorers who followed them, and the Anglos of Territorial days.

If designation as a national heritage area provides a bump to the local economy, fine. But the value of enhancing sensitivity to the place we call home goes well beyond dollars and cents.

Knowledge of the past enriches our lives in the present. It grounds both the native and the newcomer with a sense of place that, ideally, encourages us to preserve it for future generations. It's a way to acknowledge the importance of the place we inhabit, and, in a figurative sense, to allow that landscape to speak back to us.