California's largest glacier, the Hotlam, on Mount Shasta

The Hotlum Glacier is a glacier situated on the northeast flank of Mount Shasta, in the US state of California. It is the largest and most voluminous glacier in California, although not as thick or long as the nearby Whitney Glacier.

In 2002, scientists made the first detailed survey of Mount Shasta's glaciers in 50 years. They found that seven of the glaciers have grown over the period 1951–2002, with the Hotlum and Wintun Glaciers nearly doubling, the Bolam Glacier increasing by half, and the Whitney and Konwakiton Glaciers growing by a third.

The red marks the current extent of the Hotlum Glacier. The yellow lines mark medial moraines. 

As all glaciers at this latitude have done over the last several millenia, the Hotlum Glacier has receded. This has left the medial moraine isolated from the ice that created it. Nonetheless, the geology is still evident and it is easy to envision how much larger the glacier was in the not-too-distant past. If we accept the terminal moraine, which lies at the end of the medial moraine, to represent the full extent of the glacier’s size, then the massive ice sheet would have extended almost 6 miles down Mount Shasta, descending 7,500 feet over its journey. This would have been a truly staggering chunk of ice.

Mount Shasta is home to the 4 largest glaciers in California. On the northern slopes one can observe the Whitney and Bolam Glaciers while on the east side are the Hotlum and Wintun Glaciers. Of these two eastern glaciers, the Hotlum is the most notable because it is California’s largest glacier. The vast field of ice extends 1.25 miles down the side of the mountain, descending about 3,000 feet. Measuring the combined width of its multiple lobes, the Hotlum Glacier is nearly 1 mile wide at its base. It really is a singularly impressive sheet of ice. Yet, despite being notable for all of these reasons, there is another reason, more difficult to discern and more mysterious than the others. This is the fact that the Hotlum Glacier is the only glacier in California to have an extant medial moraine.