I lived in Henderson, NV for ten years and I can tell you the pickings are pretty poor and anything worthy is a long way off. I left in March 2010, so my knowledge is pretty recent.
First up, staying in Mesquite seems "central" but you are stuck with only two ways to go--north on I-15 or south on I-15. I take it you will be on the cruiser in the avatar?
(edit: I re-read your post and saw the reference to the ST
) So, big twisties will not be your main concern (just a guess). Weather should also be considered as Mesquite and both directions on I-15 for quite some distance is desert. In summer, expect temperatures exceeding 100°F to be the norm.
Going north into Utah is the better choice of the two. Beware of the Utah State troopers who lie in wait for the un-suspecting just entering their state, so watch your speed.
I consider the part of I-15 between Littlefield, AZ and the Utah border to be very Dolomite like in that the geography is right next to the road. Cliff faces, hundreds of feet straight up on both sides of the road.
Speaking of Littlefield, there is a road from there that circles its way around to St. George, I have not been on it, but might be worth a look.
Zion is very expensive to enter for only about 20 miles of road, $25 per vehicle. I never paid the price, so my knowledge of Zion is non-existent really.
A really nice ride might be for you to head for Dixie National Forest, east of Cedar City. All of the roads are paved (not sure about 148 though), lots of trees and very high elevation. You will go above 10,000 ft., so be ready for that. I put a post of the (all) day ride I did in August 2009 on the
Aprilia forum that will give you an idea of what you will see. We did not go through Zion, but took the rather mundane route of UT59/AZ389 into Fredonia, Arizona (Hail! Hail Fredonia!). Between Hurricane and Fredonia you will see areas of habitation that will make you wonder why anyone would want to live there! If you take US89 south out of Fredonia, you will be heading for the North Rim of the Grand Canyon when you turn on to AZ67 at Jacob Lake. I know nothing of gas stations along that route, sadly. But the North Rim is not as heavily visited as the South Rim and it does give a different view.
Points south: Okay, there is Vegas, The Strip is The Strip with free parking at any property on The Strip. You pay to park downtown. There is a road called "Frank Sinatra" sandwiched between the I-15 and the various Strip properties next to I-15--use it! Drive The Strip once, only to say that you have and then never do it again! The Strip officially runs from Russell Road on the south end (Mandalay Bay) to Sahara Ave. on the north (Sahara Hotel/Casino closes on or about 16 May, Vegas is really feeling the pain of the economy. I should know, I'm one of the many people that were let go). There is another road that runs behind the properties on the east side of Las Vegas Blvd. called "Audrie," look for it too.
On the way to Vegas is the Valley of Fire, just a little sight seeing there with rocks that seem to be "on fire," hence the name.
Red Rock Canyon, at the foot of the mountains on the west side of Vegas is very busy and only good for the sights, not much else.
Mt. Charleston is a nice escape from the heat of Vegas as the road climbs above 8500 feet, but it is heavily patrolled by you-know-who which really cramps a persons riding style. Also, there are no gas stations in Mt. Charleston, so be sure you have enough before leaving US95.
Death Valley is not that far beyond Vegas, but going there at any time other than winter on a motorcycle is pure folly.
North of Vegas, on US93 is the junction of NV375, "The Extraterrestrial Highway" and the rather infamous road entry into "Area 51." My brother and I did this trip in the car. The road itself is this very long stretch of gravel road that is very well maintained (a dead give away), but kicks up a ton of dust. It may not look it, but it is over 13 miles before you get to the "no trespassing" signs and the white Chevy Avalanche (it is not a Jeep Cherokee anymore) parked on the hillside. That hillside spot also lets them see the road you just took and with the dust that is kicked up...... The signs warning of the use of "deadly force" are gone, but the intimidation level remains rather high. If you can swing it, 30 miles north of the gravel road on 375 is the town of Rachel, go if you can, especially at night! You don't know what you might see....in the air or on the ground.
Finally, Hoover Dam. I left before the dam bypass bridge was complete, so there should be an exit (or something) that will take you on old US93 down to it. Take the "hard hat" tour as I found it fun and it does take you down to the generator houses at the bottom.
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