Cahill is a travel writer who I heard about from this interview with the San Jose Mercury News... which noted that he just finished a semester teaching at SJSU. This being enough to send me scurrying off to the library, I found "Lost in My Own Backyard", published in 2004 about Yellowstone National Park. Cahill notes right from the start that it's not intended as a guidebook, but rather his reminiscences on time spent there.
It was a good and very short read which if I lived closer to Yellowstone would make me want to go spend time there (likely the intent of Cahill). With my being in Northern California, though... Cahill's short book made me want to go back to Yosemite (which I also suspect the author might well be pleased with as a result of his work).
The easy comparison to make is of Cahill to Bill Bryson (author website here) and while I find Bryson to be funnier (and I suppose more entertaining as a result), Cahill's writing is solid in that it's able to inform without being dry on the subject at hand.