Therefore it stands to measure that such volcanically active regions, such as Mt. St Helens, and all volcanic Islands, should be avoided like the alien plague that they are. Is it coincidence that such areas have abduction and alien sighting rates 25% higher than average? These huge complexes are used for every conceivable function that the invading aliens need, including weapons and starship manufacturing, facilities for experiments, and alien R&R (which is said to involve certain country music stars, who have long been replaced on the surface with alien duplicates.) However, hundreds of smaller alien bases exist, tunneled through shallow dirt and rock, some of them only a few miles in diameter. The dirt and rubble removed in their excavation is commonly sold as "fill dirt" by alien-controlled landscaping firms.
In conclusion- stay away from volcanoes, both extinct and active! However, even then, there could be an alien base in a neighborhood near you.
Saucer-shaped craft silently rising from gaping holes in the earth
A sudden drop in the water table
You notice that the boss of a local quarry has the tendency to laugh maniacally and rub his hands fiendishly when he thinks he is alone
Tremors in the earth
Footprints leading from the mutilated corpse of your prize cow to a gaping shaft straight down through solid rock
An increase in sightings of strange lights in the sky
Under hypnosis, you recall being rolled on a gurney down a long metal tunnel, deep into the earth's core
A small, yet sinister, excavation similar to this: