Your best rental options are limited to the larger cities (especially San Fransisco). Within the park, The Ansel Adams Gallery rents some equipment, but is geared for enthusiasts and not on par with Zone VI monster pods. I believe they rent lighweight tripods for $7 per day (Goldcrest? brand). If you plan carefully, you could ship your tripod via FEDEX Express Saver (they only guarantee two-day delivery to the park anyway) or UPS which delivers to the Ansel Adams Gallery daily M-F, and then ship it back home when you are done. More expensive perhaps, but less of a hassle?