Pretty much anything and everything. Really cheap ones can be made out of high tensile steel(hi-ten), slightly less cheap one would be Cr-Mo(chrome- molybdemium). Then there are aluminum bikes, titan bikes, carbon fiber bikes and a bunch of oddballs,
Strength
weight
cost
Requirements for machining and joining
materials compatibility with other parts.
Type of bike to be used for
Weight
Cost
Stiffness/Strength
Requirements for machining and joining
Compatibility with other parts
Any material can be used to make a sturdy frame. Its all a question of what dimensions are used.
Mountain bikes are designed to be ridden on rough and unever terrain. Because of this you will want to find a bike that is durable and has both appropriate shocks and tires.
Strength.
Weight.
Corrosion
Machining
Mountain bike frames are made from a variety of different metals. Some sturdy frames are made from titanium alloys, while others are made from steel. Lightweight mountain bikes may also be made from aluminum.
Most modern bicycle frames are made of one of three components: Aluminum, Steel or Carbon Fiber. Aluminum can make for a more forgiving frame. Steel frames are hardy, transfer power well and are commonly found on BMX bikes and some mountain bikes. Carbon Fiber frames are the lightest and most expensive frames and are only found on the high end road bikes.
Honda
It seems that the frames are made in Taiwan, then sent to Colorado, where they are inspected, and the rest of the parts are fitted.
The first hit I get on a net search is a company that make hand buillt titanium frames. If those are the vertigo bikes you are referring to they are likely to be really, really good.
Basically the same as road bikes, but with thicker tubes and bigger welds.
Most mountain bikes are made from Aluminum, some are made from carbon fiber and older bikes are made from steel. Quality, weight and strength vary hugely by manufacturer with most high end bikes claiming unique methods which either reduce weight, improve strength or both.
Cannondale metal bikes are most likely aluminium frames.
Yeti bikes are sturdy bikes that are manufactured for mountain riding. They are made with stronger parts and brakes that can withstand the rugged terrain.
bmx's are made for trick and stunts and only have one gear & they don't have suspention they are also smaller , mountain bikes are more for terrain because they have gears and suspention and are a bigger
Orange Mountain Bikes was created in 1988.
The Giant company has been making bicycles for over 40 years, making them an experienced company. Some advantages to their mountain bikes include their high end aluminum frames, their use of composite materials, and their light weight while maintaining high ride quality.