Dennis Johnson was born in Los Angeles on 19 November 1938. His parents, Elouise and Wilbur Johnson were of Scotch-Irish and Swedish descent. His parents had divorced by the time Dennis was six. He was a bit of a troublemaker and his relations with his new stepfather were sometimes strained. Dennis has two half-siblings, Judith, born in 1944, and Don, born in 1948 on Dennis’ 10th birthday.
Dennis lived between Crenshaw and Western Avenues until his sophomore year at Canoga High School in the San Fernando Valley. That was followed by two years at Phillips Exeter Academy in Exeter, New Hamphsire. Dennis began college in 1956 with four quarters at California Institute of Technology but decided to transfer to University of California, Los Angeles, partly for musical reasons.
Dennis is considered by some to be the founder of minimalism in music, and this story is well told in [e2]. His obituary in the New York Times (see nytimes.com/2019/01/09/obituaries/dennis-johnson-dead.html) gave special emphasis to his musical work, and his four-hour-long composition November is considered a modern masterpiece.1
Eventually Dennis settled down into mathematics and wrote a Ph.D. thesis entitled “The homology of locally finite CW complexes” withas adviser, finishing in 1968. Knowing Dennis, I’d guess that the research was independently done. And it was good enough that Dennis got a two-year post-doc at the Institute for Advanced Study from 1968 until 1970.
I was an assistant professor at UCLA while Dennis was a grad student, and I must have seen him, but all I recall hearing about him was that he believed that the Chinese had once known the art of making themselves invisible, but had lost it down through the ages. When I asked him about this years later he thought a bit and then said he could imagine how that story might have gotten started.
I spent fall 1968 and also fall 1969 at the IAS, and I think it was the latter year when a few of us, probablyand , were discussing rock climbing and planning a trip to Ralph Stover State Park, the local practice area just over the state line in Pennsylvania. Dennis overheard us and asked to come along. That’s when I really got to know Dennis, and it was the start of an intense ten years of rock climbing and then whitewater kayaking together.
Dennis returned to Los Angeles and rather than pursue an academic career, he took a job involving planetary exploration at the Jet Propulsion Laboratory in Pasadena. He also took up rock climbing with his usual intensity and enthusiasm. The best local practice climbing in the area was at Stony Point in the northwest San Fernando Valley, where there was a nice bunch of house-sized sandstone boulders. Further away was Tahquitz Rock near Mount San Jacinto. Tahquitz was where the soon-to-be-famous climber Royal Robbins learned the sport, started the decimal system for rating climbs, and put up some of the hardest routes of the time. Some 10–15 years later, Dennis climbed almost all of those classic routes, e.g., Innominate, Chingadera, and others. I joined him on some of the climbs, and he came up to Yosemite after I went to Berkeley in 1972 and joined Mike Freedman and me on other climbs.
Both Dennis and Mike had independently tried the classic Northwest Face of Half Dome and failed through insufficient planning. In 1975 they decided on another try and took me along for additional common sense. We spent four days on the climb, hauling eight gallons of water and additional gear, and were uneventfully successful. They were the stronger climbers, but gave me the last two (easier) pitches as a consolation prize. (The reader can view Half Dome’s famous “Thank God Ledge” from above in the this YouTube video.)
Jim Kister and a contemporary of ) had meanwhile come to California in the early 1970s. He’d had some kayaking experience and knew how to make a kayak from a mold. In 1975 he encouraged me to make one from a Mark IV mold, using fiberglass cloth and a resin. We did so, and Dennis heard about this so we made another for him. That started five great years of whitewater kayaking with Dennis. (Rich did not pursue the sport, for his interests lay in constructing things, such as very good violins, wind surfers with hydrofoils, etc.)(fine topologist, Ph.D. student of
In the great droughts of 1976–77 and 1977–78, we did not do so much river running, but we did learn on our own how to run low-water rivers. We also discovered that our homemade boats were brittle, and tended to break after hitting rocks. So we borrowed the mold again and used Kevlar and epoxy. Kevlar is extremely tough and epoxy worked much better than the earlier resin, so our kayaks did not break. But they did develop soft spots, and thus required repeated applications of extra material to stiffen them up.
In 1978, the first plastic boats appeared. They were called Hollowforms and were made out of the equivalent of garbage-can plastic, and so were quite tough. If bent, they simply returned to their original shape. With this development, the sport suddenly opened up and rivers that were previously unrunnable (from a multitude of rocks) became doable.
It was quite exciting to be in on the beginning. Ordinary people like us could, with a bit of determination and daring, do first descents of serious rivers. Over the course of two days in May 1980, we descended the upper portion of Mill Creek, fed by snows on Mt. Lassen. It was a fantastic run, and when we finished I declared this was going to be our best run ever, for it was so unlikely that we would be able to match it in the future. This declaration has held up.
Three of our competitors for first descents were Lars Holbeck, [e1]. Their description of the Mill Creek run starts out:(UCSC geometer now, but a high school student then), and Chuck Stanley, and they outdid us. Holbeck and Stanley edited the “Bible” of whitewater kayaking in California, Guide to the best whitewater in the state of California
Check out that gradient. This has to be some of the steepest runnable whitewater in California. The average gradient over the 17 miles is 135 feet per mile, including 5 miles averaging 200 fpm. When I first looked at this run on the topo maps, I thought, “No way; no how; like never!” I was shocked when I heard that Dennis Johnson and Rob Kirby ran this section in 1980 with no portages!
Our other most notable first descents were both legs of the Clavey River, a tributary which, when it hits the Tuolumne River, causes Clavey Falls, the hardest rapid on the classic “T”. Dennis and I took three days to run the lower half of the Clavey, and portaged 23 times, so you might say we only ran/walked the run. In the “Bible”, Holbeck writes:
Before 1984, the Clavey was shrouded in mystery. In 1980, Dennis Johnson, that tight-lipped pioneer of many “secret” runs, ran the two sections of the Clavey with Rob Kirby. […] Allegedly they took two days on the 8.8-mile lower run, portaged over 20 times, and subsisted on only a few peanut butter sandwiches.
Holbeck et al. eventually gave it a try in 1984, and being better boaters, ran it with fewer portages. His comment about Dennis being tight-lipped and secret refers to an important part of Dennis’ kayaking philosophy. He felt that there was something pure and mystical about a first descent. If you heard that a section of a river had been done, then you knew it was possible, that it had no death traps, that this virgin river had been deflowered. So Dennis did not want to rob others of the joy he felt in a first descent, and thus tried to keep them secret, sometimes successfully.
Dennis burned out on kayaking in May 1981. The intense joy of kayaking could not keep increasing, and he only came back to social kayaking decades later.
In the time span that corresponds roughly to those kayaking years, Dennis did his most notable work in topology, particularly on the Torelli subgroup of the mapping class group of a surface. (This is the subgroup of diffeomorphisms that induce the identity on homology groups, and is generated by Dehn twists on curves that bound or opposite twists on pairs of curves that co-bound.), responding to a Math Overflow question, referred to Dennis and his work with these words: “ ‘A Survey of the Torelli Group’ by Dennis Johnson (the crazy genius behind much of the foundational work on the Torelli group).”
Dennis might drive 1000 miles on a four-day weekend from his three-day-a-week job at the JPL, and during that time he thought hard and successfully about topology. Whenever we met, and during shuttle runs from take-out to put-in for some river or other, he would tell me with genuine passion and intensity about his mathematical work.
After 1981 I didn’t see Dennis much, but I know he continued rock climbing, sometimes withHe became interested in restoring old silent films, particularly those starring Clara Bow, the “It” girl. He moved to Oakland in time for the famous 1991 Oakland Hills fire, which burned up his studio apartment and his trove of kayaking photos.
Very sadly, dementia enveloped him in his later years. Dennis stayed for a time in assisted living in the East Bay — healthy, skinny, not speaking or recognizing people, but apparently enjoying music. He died peacefully on December 20, 2018.