Like many mushrooms, morels can grow at different altitudes and in different places. However, the key to finding them is often in knowing where they are most likely to be abundant. Armed with this knowledge, a person is more likely to find them, though they may also grow in other places.
Morel mushrooms are primarily forest mushrooms, and they prefer mountainous terrain. While they can occasionally be found growing in low altitudes near deciduous forests of oak and maple, they are more abundant in coniferous forests of fir and pine, or mixed forests that include such trees as aspen and cottonwood. They are also more likely to be found at elevations above 3500 feet, and especially those around 5000 feet.
A great deal of this has to do with the optimum growing conditions for the fruiting body of the morel; what most people think of as a morel mushroom. The hair-like roots are also morel mushrooms, however they are hard to see, and they won't always send up the morel we are used to picking and eating.
These mushrooms need a lot of good nutrients in order to send up the mushroom stalk. This doesn't mean that the soil needs to be rich, and in fact, morels are often known to grow in poor and rocky soil. The nutrients come from the natural breakdown of pine needles, fir needles, and leaves, laid down through the year. The tiny roots of morels actually aid in this breakdown, while absorbing the foods they need to produce the mushroom. They are one of many plants and organisms that are responsible for forest soil being so usually rich. It is a secondary benefit of the mushroom.
Morel mushrooms require moisture to grow. Forests are ideal, as there tends to be moisture there even in late spring, in the form of dew. The dew dampens the soil, and since the tiny roots are very shallow, they can have the water they need to survive. The dew can persist daily even during hot times, in a forest, allowing the roots to continue to grow and gain in strength, in order to produce the mushroom, often two or three years after the minute spore began to grow.
The spore also needs to be protected from extremes, especially wind. This is why morels are often found in areas around the base of saplings, logs, branches, and in depressions. Again, forests provide ideal locations for the spores to settle and grow, while being protected from the worst of the elements.
For the fruiting body or mushroom, though, the soil must be warm on the surface during the day, and cool at night. The forest is perfect for this, in mid to late spring, and this explains why morels often follow the snow line, as the snow melts. The thaw is usually warm during the day, and cool at night, and the melting snow provides moisture. All of this also speeds decay of the needles and leaves, which gives the roots extra nourishment to produce the mushroom.
In defining where morel mushrooms grow, it is necessary to examine why they grow there. The easiest answer is that they grow in mountain forests of fir, pine, or in mixed forests. This isn't always true, but most often, it is.