The summer image below gives a sense of where most of the glacial areas are located in the North Cascade range.
USGS 2013 image
The South Cascade Glacier has one of the longest mass balance measurement record, dating back to the 1950s (glacierstudies/scascade). Mauri Pelto began long term mass balance monitoring of several additional North Cascades glaciers starting in the 1980s (http://www.nichols.edu/departments/Glacier/). Many of those glaciers are on Mount Baker. North Cascades National Park began mass balance monitoring several other glaciers in the 1990s (nps.gov/glacial-mass-balance) in the hopes of capturing a range of glacial settings with the Park.
One of the glaciers not monitored is the McAllister Glacier, its location noted on the above image. I got a bit of a peak-a-boo view of the lower McAllister Glacier in 1990 when doing field work on the Eldorado Pluton. The view was from the sharp edged divide between Marble Creek and McAllister Creek valleys.
Views of McAllister Glacier from the west
Crevassed ice in the foreground are small hanging glaciers above the valley
The terminus of the glacier was 3,000 feet below
The McAllister Glacier is tucked away in a very hard to reach and very rugged valley with no trails deep in the core of the North Cascades. While there are hundreds of glaciers in the North Cascades, very few of them extend down into valleys like the McAllister. What is more, only the Carbon Glacier coming off of the northwest side of Mount Rainier extends to a lower elevation than the McAllister. The Deming on Mount Baker formerly reached to a lower elevation but it has receded to higher elevation terminus. The McAllister Glacier terminus is over a 1,000 feet lower in elevation than the more famous and far more studied South Cascade Glacier.
Despite its low elevation reach, the McAllister is rather poorly suited for mass balance monitoring - it is remote, the glacier is complex, much of it appears dangerous to spend time on and a fair bit of the lower glacier is fed by avalanches off the steep mountain sides above.
Dashed blue outlines are the two areas of upper glacier that feed the lower glacier via ice falls down cliffs to the lower glacier. Blue arrows note other sources of lower glacial ice via avalanches. The upper slopes above the glacier are about 8,000 feet. The glacier terminus is at currently at 4,100 feet.
Like most of the North Cascade glaciers, the McAllister has been receding.
Estimated terminus locations based on historic aerials showing ice and vegetation
Note the lake is not present in 1947 but is occupied by ice at that time
The retreat between 1947 and 1979 was moderate
The pictures I took were from 1990 and the lake was present
Substantial retreat has taken place in the 1990s and 2000s