What is mawrth?

Some articles on mawrth:

Mawrth Vallis
... Mawrth Vallis (Mawrth means "Mars" in Welsh) is a valley on Mars at 22.3°N, 343.5°E with an elevation approximately two kilometers below datum ... Mawrth Vallis is one of the oldest valleys on Mars ... The Mawrth Vallis region holds special interest because of the presence of phyllosilicate (clay) minerals which form only if water is available, first identified in data ...