With the following sentence:
We will take you from here to the top of that mountain, 10,000 feet up.
Is "10,000 feet up" considered a non-essential dependent clause? Regardless, is the comma considered a grammatical error?
With the following sentence:
We will take you from here to the top of that mountain, 10,000 feet up.
Is "10,000 feet up" considered a non-essential dependent clause? Regardless, is the comma considered a grammatical error?
Punctuation is a matter of style, so you should be guided by your manual of style.
First of all, 10,000 feet up is not a clause which requires a verb in it. It is rather an NP (noun phrase).
The comma is not a grammatical error considering 10,000 feet up could be considered as an appositive which is "of, relating to, or standing in grammatical apposition":
grammar: an arrangement of words in which a noun or noun phrase is followed by another noun or noun phrase that refers to the same thing.
[Merriam-Webster]
In your sentence, the top of that mountain is the same thing as 10,000 feet up, and 10,000 feet up is a non-essential part of the sentence. Therefore, a comma is required there to separate the two noun phrases.
You have that in that mountain, so 10,000 feet up cannot be considered essential. So your sentence is a shortened form of:
We will take you from here to the top of that mountain, which is 10,000 feet up.
Another option is that you are repeating the goal
We will take you from here to the top of that mountain.
We will take you from here 10,000 feet up.
the comma is then acting like or:
We will take you from here to the top of that mountain or 10,000 feet up.
Either way a comma comes naturally.