Several editions of this booklet are available on archive.org. The earliest one there is dated 1906 and it is completely different from this 1913 edition. The 1907 edition, however, has much of the same text as this one, though they share few if any photographs. By 1909, NP began using the cover shown here.
Northern Pacific had a near-monopoly on transportation to Yellowstone until 1907, when Union Pacific opened its line to West Yellowstone. Perhaps the pending loss of that monopoly is what inspired the northern railway to step up its advertising efforts with publication of Land of Geysers.