Across the Wide and Lonesome Prairie

Now that we're in the North Platte River Valley the air feels dry and thin. My lips are so chapped they bleed when I talk. The only thing to do is dip our fingers in to the bucket of axle grease and rub our lips every hour or so. It smells bad, it tastes bad, and the blowing dust sticks. It feels like we must be halfway to Oregon, but Tall Joe says, no, we've only gone five hundred miles. He also says the worst part of the trail is to come. Does he mean more rivers to cross...? I'm afraid to ask what he's talking about.