Respuesta :
The adverb clause in this sentence is 'if the route was too steep and dangerous'.
Answer: "if the route was too steep and dangerous"
Explanation: This whole clause, which starts with the subordinating conjunction if, modifies the verb "would take..." of the main sentence. A clause that modifies a verb (or an adjective, or another adverb) is therefore called adverb clause because of its function.