Air pressure on Earth at 6700m is around 430mBar. [0] Pressure on Mars (at the artificially defined zero-level) is 6 mBar [1] and twice as much at the lowest point of Mars' surface [2], Hellas Planitia, which is a huge crater in the southern hemisphere with its lowest point around 9000m below zero.

[0] https://www.wolframalpha.com/input/?i=air+pressure+6700m

[1] https://de.wikipedia.org/wiki/Mars_(Planet)

[2] https://en.wikipedia.org/wiki/Hellas_Planitia