FACE THE CONSEQUENCES IN NEW MEXICO ENCOUNTER A LOST LONDON ON THE MISSISSIPPI

State Route 375 – the 98-mile strip of tarmac that, thanks to its proximity to the classified US Air Force zone of Area 51, and its hoary reputation for unexplained sightings, is also known as the Extraterrestrial Highway.

The 21-day Best of the West road trip from Audley Travel (01993 460914; audleytravel.com) passes close to the NTS. From £3770pp, with flights

Aliens also flicker in the imagination of New Mexico, where Roswell’s encounter with a crashed weather balloon in 1947 gave birth to a town so obsessed with little green men that they appear on everything from soda machines to lamp posts. Yet it is not, perhaps, the strangest place in the state. That role goes to an outpost which, in 1950, got to host the 10th anniversary edition of a popular radio show, on condition that it altered its name to that of the programme, Truth or Consequences. It is, though, more than an oddity. Its position on the

Rio Grande and the existence of thermal bathing sites (such as riverbendhotsprings.com) are a reminder that the town’s original moniker was much more explanatory: Hot Springs.

The 10-day Journey through the Land of Enchantment trip from Bon Voyage (0800 316 3012; bon-voyage.co.uk) calls on both towns. From £2,115pp, with flights

Popular perception of America rarely considers sizeable settlements, dotted across its vast landscape, in the years before Columbus sailed west. But Cahokia was just that – a city alive on the Mississippi between 1050 and 1350 that, at its peak, had a larger population than the contemporaneous London. It exists today as a Unesco-listed landmark (cahokiamounds.org), tucked into the eastern suburbs of St Louis on the Illinois side of the river. That Cahokia consisted of colossal earthworks means it “only” survives as 80 or so raised mounds, but it sings of a civilisation that thrived before Spain knew it was there.

Hayes & Jarvis (020 8106 2403; hayesandjarvis.co.uk) has a 16-day Route 66 Road Trip Holiday that pauses in St Louis. From £3,499pp, including flights