Velvia should do well in southern Utah- I just bought a couple rolls for a hike in Zion NP. If you look through
Michael Fatali's galleries you can see what film he used for his shots, and most of it is either Velvia 50 or Ektachrome 100vs.
Tom Till has some great pictures in his portfolio, and when I was lucky enough to meet him he said he mostly shot Velvia. I don't have any ideas for star trails, sorry.
Which parks are you visiting?
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K10D, ZX-L; DA 14 f/2.8, DA 18-55, DA 50-200, FA 20-35 f/4, FA 50 f/1.4, K 200 f/2.5; Sigma 28-80 f/3.5-5.6, Quantaray (Sigma) 100-300 f/4.5-6.7
Diamond Bar X Photography