Goatheads are a fact of life in much of the western US and some of western Canada. We have to deal with them but you probably don't. I've been to the Picketwire about 30 times over the years and I've had rides where we didn't get any flats and the nightmare ride I detailed above. The number of goatheads in any given year are dependent on lots of different factors. Rain, drought, wet spring, dry spring, hot summer, soil disturbance, etc. all have an effect on the number and location of the plants that sprout. In the last few years there have been more forest service vehicles in the area were bicycles ride doing work that have lead to an outbreak of goatheads.

I do use puncture resistant measures. I've done rides where my measures did better than tubeless...I went the entire distance without a flat and the tubeless guy...with Stans sealant...had several flats. I've tried slimed tubes which didn't work and, personally, I find extremely messy to deal with.

As for mode of travel, feel free to walk 18 miles. Feel free to consider an 18 mile hike an "easy" distance. I don't consider it so. 18 miles on flat ground takes around 6 hours and this route isn't that 'flat'. The trip takes between 4 and 6 hours by bicycle not because it is a difficult bike ride but because there is so much to see along the route. If I walked the route, it would take the 6 hours of travel and around 4 hours for the sight seeing. That a lot of time.

And, if I wanted to hike it, I doubt that I would be posting anything about the trip in the Bike Forums