It is not an iframe. It is just a background image set to the body tag. This is their actual CSS code for body:

   body {
      font: 100%/1.3 Verdana, Arial, Helvetica, sans-serif;
      background-color: #666;
      background-image: url("https://offbeatoregon.com/assets-2010/1012b_gorge-highway-crown-point/crown-point-1800px.jpg");
      background-repeat: no-repeat;
      background-position: center top;
      background-attachment: fixed;
      margin: 0;
      padding: 0;
      color: #222;
   }