Identify rather the underlined clause is an adjective clause adverb clause or noun clause after they had traveled for several years the people settle near the freshwater source.

after they had traveled for several years - adverb clause

Explanation:

The clause "after they had traveled for several years" is introduced by after, which is a subordinating conjunction of time.

The clause "after they had traveled for several years" is  an adverb clause of time.  

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