Big Hollywood action-adventure movies have gotten so terrible that a vacuous but fast-moving example of the genre can sometimes succeed just by being better than a bad lot. That’s why in the arid wasteland of stuff like “National Treasure,” “Sahara,” based on Clive Cussler’s book, comes across like a trickle of water, if not an oasis. It’s as brainless as most pictures of its ilk–indeed, it’s almost gleefully so, in the mold of the goofiest Saturday morning serials–and never reaches the status of a picture like “Raiders of the Lost Ark,” its obvious inspiration. But it’s also breathless, moving along from set piece to set piece with a brisk efficiency that makes it at least the equal of the Indiana Jones sequels (which admittedly weren’t awfully good).

The real hero in this regard isn’t Matthew McConaughey, who strikes the right poses and an appropriately macho attitude as treasure-hunter Dirk Pitt without exhibiting the last ounce of charisma. Nor is it Steve Zahn, who mugs ferociously as Pitt’s doofus pal Al Giordano but is hobbled by the fact that the banter the quartet of screenwriters has devised for the duo never goes beyond the puerile. (The plot, which has the duo searching for the wreck of a Confederate Iron-clad ship up river in Africa, is no great shakes either.) And it’s certainly not Penelope Cruz, who fails to set the screen ablaze as Ana Rojas, the W.H.O. doctor who teams up with our intrepid adventurers while investigating the cause of a deadly plague and becomes the obligatory romantic interest. (Needless to say, her mission becomes intertwined with their search.) Even ordinarily reliable character actors like Delroy Lindo and William H. Macy pretty much coast through their roles, the former as a C.I.A. operative and the latter as Pitt’s long-suffering boss.

Nor are Cussler and the scripters the reason for whatever success the picture can claim. The basic premise about that Civil War vessel is simply absurd, and when things morph to emphasize the plague scenario–which in turn becomes the story of a toxic dump that involves a vicious warlord (Lennie James) and an ambitious French industrialist (Lambert Wilson)–the level of plausibility does not increase markedly. (Indeed, when the plot makes some limp efforts to remark on the serious socio-political situation in Africa, it seems tawdry, and when it then goes beyond the continent to depict the threat as one that involves the entire world, whatever credibility might have remained simply implodes.) And when a band of noble Taureg horsemen show up to become the good guys’ allies, things really go over the top.

No, the pleasure to be derived from “Sahara” is almost entirely to be credited to Breck Eisner, the son of the notorious head of Disney, who keeps the picture hurtling headlong to avoid those lulls where the plot holes and improbabilities would weigh too heavily on the viewer’s mind. A picture like this doesn’t need a director as much as a traffic cop, and Eisner proves adept in that capacity. He stages the elaborate set pieces, which follow one after another with little let-up, very well, and editor Andrew MacRitchie works closely with him to keep the flick chugging along over the narrative potholes. Seamus McHarvey’s widescreen cinematography uses the locations to good effect, too. A pity that Clint Mansell’s score, which could have bolstered the excitement level, is so terribly banal. Overall, though, it’s the execution that saves the day here.

Unlike its geographical namesake, there isn’t very much to “Sahara,” but if the content is negligible and even puerile, the packaging is choice. Nonetheless, that may not be enough to turn the picture into a hit. Its old-fashioned character is reminiscent of the second Lara Croft movie, “Tomb Raider: The Cradle of Life” (also edited by MacRitchie), which was dumb fun of the old James Bond school but apparently proved too passe for today’s adolescent thrill-ride audience. The same fate might behind this movie, one that those who revel in the luridness of a “Constantine” or “Sin City” might find too light-hearted and tame. That would be a pity, but it’s a serious possibility.