The army was there. But after the initial attack. They were a releiving force along with the 2nd Marines.
"In November 1942, when the Japanese Army gave up hope of retaking Guadalcanal, and the Japanese Navy ceased trying to send reinforcements, the bloodied First Marine Division was withdrawn. Meanwhile, the 164th Infantry and the 2nd Marines had arrived. These were elements of the Americal Division of the U.S. Army and the Second Marine Division."
*****
When the Guadalcanal campaign began, it was the first land offensive by the United States against any Axis power. It continued to be the only land offensive by the United States until the major Allied invasion of North Africa in November 1942. Under the "Europe first" doctrine of the Allied leadership, the material for Guadalcanal was assigned grudgingly. This made it "Operation Shoestring" to those involved. The future of the operaton was also immediately put in doubt by the disaster of the Battle of Savo Island. Nevertheless, the American public was far more incensed about Japan than about Germany and was eager for news of American attacks, after many months of American forces being defeated and captured in the Philippines, and on Wake and Guam. Thus, an account of the earliest days on Guadalcanal, Guadalcanal Diary, by combat reporter Richard Tregaskis, was a sensation, and a reasonably faithful movie version was turned out within a year (even if obviously shot in California). The land fighting on Guadalcanal was also immortalized in James Jones' The Thin Red Line, made as a movie in 1964 and recently remade by Terrence Malick in 1998.
The fighting in The Thin Red Line, however, comes from fairly late in the campaign, after the Battles of the Tenaru River, Bloody Ridge, and Henderson Field. All the early fighting was right on the perimeter of Henderson Field, with the Japanese trying to break in during night attacks. The Japanese had trouble appreciating the seriousness of the American threat. The first Japanese attack, led by Colonel Kiyono Ichiki, was the result of serious material and moral miscalculation. The Japanese believed that about a regiment of Americans had landed, not the better part of a division. Ichiki's regiment was thus sent to retake the island. Since Ichiki also believed that one good surprise night attack would cause the Americans to run, he did not even wait for his whole unit but advanced with no more than a battalion. He didn't even have the advantage of surprise and so died with nearly all his men. The next Japanese commander, Major General Kiyotake Kawaguchi was more prudent, using his own regiment and the remnants of Ichiki's with more care. He still gravely underestimated the American forces, however. The Battle of Bloody Ridge, although harrowing for the Marines, nevertheless gained the Japanese nothing of their objective.
*******************
http://www.friesian.com/history/guadal.htm