Yeah, but this is Sam Clemens we are talking about
One of the more astute observers of human phenomena. Not some fly-by-night documentary producer or one of your modern journalists who has the story written first and then looks for sound bites to back it up.
Frankly, I'd take his word over my own personal observations, unless I observed with care for a long time. And I don't say that about many.
And he's not alone in that observation. On the other hand, there weren't a lot of witnesses to the lack of people there because, well, there weren't a lot of people there to note the lack of people. It's a freakin' dessert. Sand. Rocks. Not much else until people put something there.
