Mount St. Helens
Mount St. Helens
[Caption above graph:] Heights of mountains in Washington State Over time
[A graph is shown with close to 30 horizontal gray lines which seem not to change much, if any, as they go from left to right. Only the top 6 gray lines are distinctly separated from others. The top line is way above the second line which again is far above the next two that are close together. Two more close together is somewhat further down, and just below them the rest of the lines follow in close proximity down to the bottom of the graph. A single black line is also shown. It begins as the fifth highest line, just above the two last mentioned above. It, like all other lines, goes horizontally, but only three fifths of the way across the graph – then it immediately drops down well below most of the other lines (at 1980) and levels off, continuing on its horizontal path. There is a caption above the graph, and both Y-axis and X-axis has labels. For the Y-axis there is a tick for every label, for the X-axis only every 2nd tick has a label. A unit is given on the top label on the Y-axis.]
[X-axis:] 1920 1940 1960 1980 2000 2020
[Y-axis:] 15,000 feet 14,000 13,000 12,000 11,000 10,000 9,000 8,000

This comic marks the 40 year anniversary of the May 18, 1980 eruption of Mount St. Helens that killed 57 people. It was a Monday so a normal release day could be used to mark this event.
It shows a graph of the height of the mountains in the state of Washington as a function of time over the last 100 years. The only mountain to change its height significantly over this time period is Mount St. Helens , which the comic is named after. It is also the only black line as all other (30?) lines are gray.
Mount St. Helens is a volcano that famously and explosively erupted in 1980. Millions of tons of earth were blasted from one face of the mountain all over the surrounding countryside.  After it was over, the peak of Mount St. Helens was no longer the 5th highest in the state of Washington , having lost approximately 1,300 feet (400 m) in height (from 9,677 ft (2,950 m) pre-explosion to 8,363 ft (2,549 m) post-explosion).
The comic shows a rare event that had major effect and was predictable in hindsight, but would have surprised an observer that is just tracking the height of Mt. St. Helens in a non-representative timeframe. Such an event is called a Gray Rhino event.
Currently, the 5 highest mountain peaks in Washington State are Mount Rainier (at 14,411 ft or 4,392 m), Mount Adams , Mount Baker , Glacier Peak , and Bonanza Peak . As shown in the comic, Mount St. Helens was the 5th highest, but now has fallen to #35 (using a topographic prominence cut-off of 500 m (1640 feet)). Only mountains above 8,000 feet (2,438 m) are included, with the graph topping at 15,000 feet (4,572 m), 600 feet (182 m) above the highest mountain. There are 92 peaks above 8000 feet in the state, so not all are included and the lines are not really distinct below 9000 feet. Seems like there are less than 30 lines drawn. Of course it says Mountains not Mountain peaks, but there are only four mountain ranges in Washington with peaks above 8000, so he must mean peaks!
Technically, the other mountains may be fluctuating in height as well, due to erosion or the movement of Earth's tectonic plates, but this phenomenon should not be visible on the time-scale and vertical resolution that Randall has plotted.  Precision GPS measurements of various peaks in Washington have only been available since 2010, and it's likely that the primarily volcanic mountains of Washington experience significant but comparatively slight variations throughout the year due to snowfall, melt, or the pressure of swelling magma inside volcanic cores.  These changes go largely unmeasured, while the mountains continue to appear equally physically unchanging and imposing both in person and from a distance.
Source: Seattle Times . So while the comic does appear to show some slight fluctuations in height for mountains, that is more likely a side-effect of the comic's free-hand drawing style than an accurate reflection of any real fluctuations.
The title text is a play on the term "peak" meaning both the highest point of a mountain and also the optimal, most famous or most impressive stage of a trend; for instance: "The band Rolling Stones really peaked in the 80s."
[Caption above graph:] Heights of mountains in Washington State Over time
[A graph is shown with close to 30 horizontal gray lines which seem not to change much, if any, as they go from left to right. Only the top 6 gray lines are distinctly separated from others. The top line is way above the second line which again is far above the next two that are close together. Two more close together is somewhat further down, and just below them the rest of the lines follow in close proximity down to the bottom of the graph. A single black line is also shown. It begins as the fifth highest line, just above the two last mentioned above. It, like all other lines, goes horizontally, but only three fifths of the way across the graph – then it immediately drops down well below most of the other lines (at 1980) and levels off, continuing on its horizontal path. There is a caption above the graph, and both Y-axis and X-axis has labels. For the Y-axis there is a tick for every label, for the X-axis only every 2nd tick has a label. A unit is given on the top label on the Y-axis.]
[X-axis:] 1920 1940 1960 1980 2000 2020
[Y-axis:] 15,000 feet 14,000 13,000 12,000 11,000 10,000 9,000 8,000
