Workers plant vines at Quinta do Crasto, in the Douro Valley of northern Portugal. The region is famous for port and, more recently, for red and white table wines. (Leah McIntyre)

The Hyundai tractor’s talon slammed into the rock again and again, chopping large pieces of schist into smaller ones. It resembled a bucktoothed dinosaur attacking its prey. Then the driver rolled back and forth over the debris, using the vehicle’s treads and weight to grind stone into soil. When he found a piece of rock too big to chop, two men followed with jackhammers and dynamite to blast Mother Earth into submission.

This is how vineyards are planted today in northern Portugal’s Douro Valley. Since Roman times, man has chiseled away at the schist and created vineyards terraced row by row up the steep hillsides. These are the vineyards that produce port, the fortified wine named for Porto, the city at the mouth of the Douro River where the wines are aged and shipped around the world. For the past two decades, the region has produced some of the world’s most interesting dry red and white table wines.

The vineyard I saw being created that sweltering June day stretched from 550 to 600 meters in altitude and crested a hill overlooking a bend in the Douro. Manuel Lobo de Vasconcellos pointed down toward the river, where Quinta do Crasto, the winery where he is chief winemaker, sat perched on its own hill. From this perspective, the Crasto hill seemed insignificant, though it was an old Roman outpost and site of some of the region’s best vineyards.

“At this altitude, we see the soils turning from schist to granite, and that’s better for white wines,” Lobo de Vasconcellos explained as we turned this way and that to shade ourselves from the blazing summer sun. The Douro is famous for red wines, but this vineyard was being planted with rabigato, viosinho and verdelho, three white grapes indigenous to Portugal. White wines — crisp yet floral — are the rising stars of the Douro.

Looking over the spectacular scenery, we could see a patchwork of old and new. Traditional terraces, their walls made of schist torn from the hillsides, stretched more or less parallel to the river, while newer vineyards, planted with the use of modern heavy equipment, ran in vertical rows up and down the hillsides. Older terraces, abandoned and never replanted after the phylloxera epidemic of the late 1800s, lined shadier parts of the unpaved road back to the valley.

“The Douro is a puzzle with many different pieces,” Lobo de Vasconcellos said as we tasted some Crasto wines back at the winery. Table wines, as opposed to port, became popular in the Douro in the mid-1990s, but most wineries continue to work with traditional Portuguese grape varieties. Crasto’s Maria Teresa, its top red wine, comprises 49 different grape varieties, “and they behave differently every year,” he said.

Some wineries have planted new vineyards to single grape varieties, such as touriga nacional, in the hopes that a recognizable varietal wine could establish the Douro’s identity with consumers. Others prefer to work with the mishmash of varieties their forebears planted. Modern DNA testing has identified 248 grape varieties in Portuguese vineyards, says George Sandeman, head of public relations for Sogrape Vinhos, Portugal’s largest wine company, which owns Casa Ferreirinha in the Douro. Ferreirinha includes the Quinta de Leda estate and winery, with 160 hectares (nearly 400 acres) of vineyards planted in the Douro Superior, near the Spanish border, as well as 500 hectares (1,236 acres) of vineyards in “old Douro.”

“We like the chaos,” says Francisca van Zeller, whose father, Cristiano, is chief winemaker at Quinta Vale D. Maria and his own VZ label. “As my father says, the truth of the Douro is best expressed in chaos.” The van Zellers emphasize traditional methods, including treading the grapes by foot in concrete vats called lagares.

As the Douro matures as a table-wine region, questions of style are emerging, just as they are around the world. The Douro’s hot climate and schist soils are ideal for bold, deeply colored red wines, but at least one winery owner argues that the region should not exaggerate those characteristics.

“It’s easy for us to get powerful wines with great color and high alcohol, but we should be trying to make wines with freshness and elegance,” says Dirk Niepoort, owner of Niepoort Vinhos, a stone’s throw across the Douro from Crasto but an hour’s drive away. “That is the challenge.” Niepoort was one of the wineries at the vanguard of the table wine movement, and its owner is now questioning some of the stylistic choices of his colleagues.

He is a Burgundy fan, and he makes some of his red wines with a pinot noir sensibility. That’s quite risky given the heft that Portuguese varieties attain. Yet his wine called Charme, named for the Charmes-Chambertin grand cru Burgundy vineyard, is delightfully nimble, showing the trademark portlike flavors of Douro red wines with the lightness and clarity of a tuning fork striking a pitch-perfect high C.

Just when I thought I understood Douro wines, Niepoort made me reassess. One more reason the Douro is as exciting a wine region as it is beautiful.

McIntyre blogs at dmwineline.com. On Twitter: @dmwine.