I have since discovered that he died in a mental institution from dementia.
From Sue Christenson:
Frank held various business positions during his lifetime, such as bookkeeper, mine operator, secretary/treasurer, vice-president of a mining company. In his later years, he suffered from senility and spent his last years in a state hospital. A nephew took care of his affairs, which
included his house. The balance of his mother's estate went to pay for his medical care.