The account of Andrew's death, gleaned from an account contributed to the Fort Collins Courier, April 3, 1914 by William Wallace Sullivan, Andrew's brother:
"In September, 1876, an Indian fight occurred on the North Platte river, between Fort Laramie and Fort Fetterman, in which the Indians were worsted and left to get back to their reservation at Fort Robinson on foot. Most of the whites engaged in this skirmish were former Larimer county cattle men...including Joseph Sullivan (brother of Andrew), Andrew Sullivan...the Indians had raided the stock of the Walker & Johnson ranch on Bitter Cottonwood and a posse was made up to follow them and recover the stock. "The whites followed the trail to the top of the mountains overlooking the Platte. There Andrew Sullivan went to the top of the hill and surveyed the country through a fieldglass. He discovered a bunch of stock on the Platte bottom, and it was decided that they could be none other than the ones they were after...It was agreed to dash down the canyon and cut off the stock from the Indians." At a signal given by one of the posse, "the whites dashed down the canyon and were between the Indians and the stock in a short time...made the mistake of shooting the Indian who had started after the stock. Immediately every Indian disappeared in the sagebrush. A long range fight ensued...lasted until night put a end to it. Only one white was hit, but at least two Indians were killed, including one who was shot by Andrew "almost to a certainty"... "The Indian ponies were disposed of by lot, and Andrew Sullivan got first choice. He was riding this pony from Abner Loomis' ranch on the Sabille to the ranch of Graham & Sullivan on the La Bonte about three weeks later, when he ran into Dull Knife's band of about forty Indians and was killed after a gallant fight at the odds of 40 to 1."