Our diarist is referring to the Utah War. The Mormons fled persecution in the US to the northern part of Mexico only to find it absorbed in the US at the end of the Mexican War. The Mormon practice of polygamy was considered barbaric and another pernicious result of Douglas’s popular sovereignty. Eventually even Douglas condemned its practice in the territories. Buchanan was dead set against it and was determined to bring Utah into lawful US administration. An expedition was dispatched from Fort Leavenworth to escort a new non-Mormon Governor. The expedition is now in winter camp in a bleak part of SW Wyoming near Fort Bridger, which the Mormons had burned down. The force had been weakened to leave enough troops at Leavenworth to deal with the Kansas troubles surrounding the Lecompton Constitution. How often have we seen the Army tasked to do too much with too little?
The country between Fort Bridger and Salt Lake is daunting, to put it mildly. The Wasatch is an incredible physical barrier.