First of all, I will provide the explanation of the term détente. Detente refers to a situation or policy that involves easing in political relationships, after a period of tensions.
In the context of the Cold War, the US adopted the policy of detente which put an end to the hostilities between the Easter and Western blocs. This was a result of the domestic reforms that the URSS implemented within its territory and economy which eventually resulted in the end of Communism in Europe and to the dismantling of the Soviet Union.
Answer: I would have to say the first one. Because saying that I live in Nevada, I know that they had to build to the Rocky Mountains, and the Sierra Nevada's.