Joe Biden's mental capacity to govern the country could be questioned again after making yet another mistake and claiming during a speech that the Grand Canyon is one of the "nine wonders" of the world.

The president was giving a speech Tuesday at Red Butte Airfield in Arizona, very close to the Grand Canyon, when he made the statement about the natural formation.

"Folks, it's not hyperbole to suggest that there is no national treasure, none, that is grander than the Grand Canyon. The Grand Canyon, one of the Earth's nine wonders, wonders of the world, literally. Think of that. You know, it's amazing. An enduring symbol of America to the entire world," he said.

Biden later tried to correct his mistake by assuring that he meant to say "seven" instead of "nine," also including the formation in the list of monuments.

The wonders of the world

The list of the wonders of the world states that there are only seven locations that fall into this classification and include: the Great Wall of China, Chichen Itza in Mexico, Petra in Jordan, Machu Picchu in Peru, the Christ the Redeemer statue in Brazil, the Colosseum in Italy and the Taj Mahal in India.

There is another important list that does include the Grand Canyon. However, this classification is about the natural wonders, and as in the previous list, only seven are counted: the aurora borealis, the Great Barrier Reef, the port of Rio de Janeiro, Mount Everest, the Paricutin volcano in Mexico, Victoria Falls and the famous natural formation in Arizona, Nevada, Utah and Colorado.

Another mistake during his speech

During Tuesday's speech, Biden made another error, apparently a reading error, when he said that the Grand Canyon is a "haven of ironic species" rather than "iconic."

"These lands also support a range of ecosystems and plants from savannas to sagebrush to ponderosa pine, a haven of ironic species like bats, bison, bighorn sheep and nearly 450 kinds of birds, including the bald and golden eagles," he said.

Doubts about Biden's capabilities

A recent NBC News poll revealed that nearly seven in ten respondents (68%) do not see the president as fit to lead the United States for four more years, and these types of mistakes could continue to increase that number.