With increasing altitude vegetation becomes more varied and abundant, until the tree limit is reached; then follows a forest belt, which in the highest mountains is limited above by cold as it is below by aridity.
But during the summer, temperatures are affected as much by altitude as by latitude, and the coast is cooled at night by breezes from the Gulf.
There was nothing to see at this altitude, but he wasn't seeing anything in the book anyway.
Southward the altitude falls, Death valley and Coahuila valley being in part below the level of the sea.
The first day was behind him, his muscles weren't overly sore, he seemed to be adjusting to the altitude and he had conquered more hills in one day than a year of Pennsylvania biking would offer.