In 16 States, Initiatives can make direct State constitutional amendments [which could contain a proposed US Constitutional Amendment]: Arizona, Arkansas, California, Colorado, Florida, Illinois, Michigan, Missouri, Montana, Nebraska, Nevada, North Dakota, Ohio, Oklahoma, Oregon, and South Dakota.
In 8 more States, Initiatives can make Initiative proposals for US Constitutional Amendments: Alaska, Idaho, Maine, Massachusetts, Mississippi, Utah, Washington, and Wyoming – bringing the total to 24.
In a further 3 States, Initiative processes are available but less forceful.