In a physical world, made of matter, and set in a universe that clearly operates by set laws of physics, all 'things' in that universe have to exist within those parameters. For example, there are known reasons as to why spiders cannot exceed a certain size. There are known reasons as to why the structure of bones in birds allows them to do things other creatures cannot do. To go beyond that (in those two cases) would mean different creatures / species arising.
With mountains, there are also laws governing the way they arise, factors determining their height etc. Asking if God could create a mountain of the Jack-and-the-Beanstalk (and some) fairy-tale variety is speculation of a totally unprofitable kind.
This question is a variation on, "Could God create a rock so heavy that even he couldn't lift it?" It starts with a false assumption, i.e., that God is not omnipotent. If you answer "Yes", that means that God is not omnipotent since he can make the rock but isn't powerful enough to lift it. But if you answer "No," that also means that God is not omnipotent since he couldn't make a rock so big he cannot lift it! In other words, the question itself is dishonest, a pseudo-question, since it begs the question by assuming God is not omnipotent.
Further, this question commits a category fallacy. It's on a par with, "What does the color blue smell like?" or "How much does the number 7 weigh?" That would be to commit a category mistake because colors don't smell and numbers don't weigh anything. They are logical impossibilities. In the same manner, this question is essentially to ask, "Can God's power defeat his own power?" This is nonsensical and a category error since the question is being incorrectly applied.
The one Being of God, the Almighty, must in all things and at all times remain true to his Being. Thus, if you had a Being whose essence was to create all things for his glory (which Christianity maintains), he would not create anything that would not - or could not - result in glory to himself. There is nothing in God's Being that requires him to create everything that possibly could be created, you see. He CHOOSES what to create and what NOT to create. He is not forced to create everything or anything. He sovereignly decrees what to create.
This is a philosophical question which has been refuted (in all its variations) over a few centuries.