Southern Nevada is warm when the north is cool and has several good rides.
Bootleg Canyon biking and hiking (no motorized travel) area is located north of Boulder City, Nv, about 20 miles south of Las Vegas. Located in small mountain range that divides Las Vegas Valley and Boulder City. These mountains are quite rocky, so hats down to local enthusiasts who have built quite an impressive network of trails (mostly singletrack) into the mountain slopes. Most of the rides are intermediate technical and you will have fun if you don't mind some loose rocks. I had quite a good time and logged about 35 kms with almost 1000 m vertical change on Thanksgiving Day doing first out and back Mother Trail with slight detour and then clockwise loop West Leg - Caldera - River Mtn. As the trails are quite tight at spots, they are not too fast, so it took me about 5 hours with several breaks to do the whole thing. Needless to say, there was almost nobody out there that day.
Here is official map of the trail system and here is my rough map. Here are rough elevation profiles, Mother out/back and clockwise West Leg - Caldera - River Mtn. loop.
Bootleg Canyon is also a good spot to stop on the way to or from California, which I did in Fall 2004, and rode a newly finished trail that connects Mother Trail with Caldera. Clickable map and fotos are here.
One tame bighorn sheep paraded about 50 m from the Mother trail.
A few views along Mother trail.
A view north towards Las Vegas from the turnaround on Mother trail.
Look south from the turnaround on Mother trail.
A dirt road crossing at the bottom of West Leg trail.
Views from the upper West Leg trail.
Panorama E-S with Boulder City from Lake Mead overlook.
Panorama NW from Lake Mead overlook, Overlook trail in the foreground, Boy Scout and River Mtn. switchbacks behing the ridge, Caldera in the basin on the right (and Vegas in the back).
Zoomed view to Las Vegas from Lake Mead overlook.
The proof that I was there, on the Lake Mead overlook.
Blue Diamond is a small town north-west of Vegas, which hosts a bike shop and a network of trails going south as far as one dares to go. I rode here on a way to California in Fall 2004. Comparing to the map I had, I rode about 2/3 of the trails in the area. Clickable map and fotos are here.