Irregular Natural Arch
Any natural arch that cannot be placed in the taxonomy in any of the
other types is considered to be an irregular natural arch. The combination
of attributes these natural arches exhibit is unusual, even unique.
It may be possible to determine how an irregular natural arch formed
from its observable attributes, but if so, either none of the standard
formation modes are involved or there has been an unusual combination
of them. A maturity attribute cannot be assigned to this type of natural