It's very hard to quantify this question, but it seems reliably certain that through most of the 1950's academia was solidly anti-Marxist, partially due to the Red Scare and McCarthyism at the opening of that decade. However, I don't think that Marxism was the initial vector of radicalization: the Beatniks weren't really Marxist ideologues, and anyway much of the radical transformation was initiated or at least invited by naive college authorities themselves. In the 1960's, campuses began to turn co-ed as part of a general trend of left-leaning liberalism throughout the middle-to-upper classes of the country, and the environment at this time appears to have been rather conducive to the growing cult of equality and diversity. From the little I know of the first marches at around this time, there were professors who supported anti-establishment students. Leftist ideologies are so often formed from this sort of snowball effect: from wanting to tear down natural distinctions like gender, it's a very short leap to opposing all distinctions. It mirrors very closely the same process of incremental insanity that one can observe in all revolutions (the French Revolution being the clearest expression of this, probably).
Further, I think it's crucial to note the contribution of the wider American ideology. In watching documentaries on 60's radicalism, the repetition by the activists that "We found that America wasn't the fair country we were taught it was supposed to be" (or statements to that effect) should stand out as profoundly telling. The Baby Boomers grew up in a time of unparalleled prosperity and abundance, but also a time of tremendous optimism and (I would argue) modernism. This generation grew up in new suburbs built from scratch, a project that overturned the urban-agrarian America that preceded it and essentially created a brand new country on top of the remnants of the old. That theme, that the new has the right to so comfortably triumph over the old, would appear to the Boomers as simply natural law, for they had known nothing else; the idea that the inheritance of one's ancestors ought to be maintained as a legacy for posterity simply didn't occur to them, and that modernist mindset (of near-fanatical insistence) has far more to do with the cultural revolutions of Levittown than with the tattered doctrines of Lenin.
Consonant with the 1950's radical break with the past, a new ideology was being developed that attempted to justify the new order. The idea of America as a place of fairness, justice, equality and everyone getting along was invented, created purely from platitudes. Of course, earlier generations all the way back to Jefferson had talked of these ideals and preached them at home and abroad, but they had understood them to be ideals that had to coexist with (and often be superseded by) the cultural and social makeup of the country's constituent communities. To them, equality of citizenship was a good, but it did not and could not eliminate the duties every citizen owed to his or her family and church and neighbors. Earlier Americans had (I think) understood that there was an "American way" (however defined), but that the American people (the
volk) preceded the American way, and that the ideal of the American way needed to be balanced with the bonds and loyalties that inevitably exist in people. Without the people, they thought, there could be no union, much less a more perfect one.
However, the American Way of the 1950's (which, really, is still with us) had no time for such understandings, and rejected (consciously or otherwise) the traditional recognition of people and communities before ideology. Ideals and dreams for this or that, not duty and propriety for country and kin, came to be identified with this New America. The Boomers were raised by not just their teachers but also
big business to believe that America wasn't a country, but an ideal, an ideal that could be changed to suit each passing fancy. And when America the country frustrated their attempts to achieve utopia (as real people, places and things always do), their first and only course of action (so implicit in their minds as to not merit debate or even consideration) would be to erase the country in the name of their ideal.
But back to the mid-to-late 60's. As a result of radical student bodies (or loud, aggressive fractions of those bodies) and timid or complicit college administrators, identity politics departments began to be founded in the late 60's and early 70's (the first women's studies department opening in 1969). This is of paramount importance because it represents an unprecedented shift in American society: the establishment would actively fund the teaching of ideas that undermined the very same establishment. How ironic that at the very same time that Mao's Cultural Revolution in China was reaching its apex, a veritable cultural revolution was just beginning in what used to be the center of American thought.
However, the far left of the generation that graduated in the late 60's (during and after the height of SDS) was probably the first major wave of the institutionalization of radicalism. Many of them entered academia first as PhD candidates and then as professors, and the influence from that point on needs no explanation. Moreover, it's at just around the time many of those radicals would have been finishing their graduate studies and creating courses of their own, and the years that the first classes of underclassmen would have been taught by identity politics departments for their entire time at college (1972-75 or so) that we see radical feminism gaining a wide following on campuses around the country.
From then on, the problem compounded itself through the deliberate indoctrination of each proceeding generation, and the constant demonization of any contrary opinion. Additionally, radicalism manifests itself so comfortably because of academia's isolation from the real world: idealism is always the likely tendency for people who never have to work or face the consequences of their ideology. We could go through the details of its impact in each department (usually the displacement of genuine thought for the benefit of institutionalized stupidity), but entire books could be (
and have been) written on the subject.