Company F did indeed organize at Mount Ida and march to Miller's Springs, Missouri, but the other companies organized in their respective counties and marched separately to Miller's Springs, where the regiment was organized on August 17, 1861. Just about any history you care to read says that -- Harrell, Hempstead, Gammage, etc., not to mention the Compiled Service Records. Here's what Regimental Surgeon W. L. Gammage wrote --

It was about this time that companies were organized in almost every county of the State, and not being called for by the government were hastening to join General McCulloch in hope of being allowed to participate in a struggle which was becoming daily more and more momentous.

Eight of these companies of infantry, organized and raised mainly in the southwestern part of the State of Arkansas, without consultation or concert of action, took up the line of march for southwestern Missouri, a distance from their homes ranging from three to five hundred miles, and on the 16th day of August, 1861, arrived at Miller’s Springs in Lawrence county, Missouri.

On the 17th day of August, the first complete organization of the Southwestern Arkansas Regiment (afterwards known as the 4th Arkansas Regiment) was effected by the following companies being sworn into the Confederate service by Lieut. Col. Dandridge McRea, to-wit: