can i use a fetchland to get a land that is both a mountain and plains?

[Jupiter]

can i use fetchland to get a land that is both mountain and plains?

[Kenji]

Not with just any fetchland, obviously -- presumably, you're talking Arid Mesa, yes? As long as it actually has those types, then sure. For example, Plateau or Sacred Foundry. Note that fetchlands only care that the land has at least one of the types it asks about. So, for example, Arid Mesa can also get a land like Godless Shrine or Steam Vents, since the Shrine has Plains as one of its types, and Vents have Mountain as one of its types.

Now, if you're talking a land that simply produces red or white mana, such as Battlefield Forge or Ancient Amphitheater -- not in this case, since such lands have no basic land type. They're neither Mountains or Plains.

Does this adequately answer your question? If not, please let me know what kind of further clarification you'd like.