Massive rockfall - Waterfall route

I found the GIS maps quite interesting in regards to this stuff, especially the one on the time of year historically that rock fall occurs.

Rockfall in this area is nothing new

Eiszeitalter und Gegenwart Quaternary Science Journal 57/1–2 179–209
Hannover 2008
Surface exposure dating with cosmogenic nuclides
SUSAN IVY-OCHS & FLORIAN KOBER

Abstract: In the last decades surface exposure dating using cosmogenic nuclides has emerged as a powerful tool in Quaternary geochronology and landscape evolution studies. Cosmogenic nuclides are produced in rocks and sediment due to reactions induced by cosmic rays. Landforms ranging in age from a few hundred years to tens of millions of years can be dated (depending on rock or landform weathering rates) by measuring nuclide concentrations. In this paper the history and theory of surface exposure dating are reviewed followed by an extensive outline of the fields of application of the method. Sampling strategies as well as information on individual nuclides are discussed in detail. The power of cosmogenic nuclide methods lies in the number of nuclides available (the radionuclides 10Be, 14C, 26Al, and 36Cl and the stable noble gases 3He and 21Ne), which allows almost every mineral and hence almost every lithology to be analyzed. As a result focus can shift to the geomorphic questions. It is important that obtained exposure ages are carefully scrutinized in the framework of detailed eld studies, including local terrace or moraine stratigraphy and regional morphostratigraphic relationships; as well as in light of independent age constraints.

Exfoliation of rock deteriorates cliffs through the formation and
subsequent opening of fractures, which in turn can lead to potentially
hazardous rockfalls. Although a number of mechanisms are known to
trigger rockfalls, many rockfalls occur during periods when likely
triggers such as precipitation, seismic activity and freezing
conditions are absent. It has been suggested that these enigmatic
rockfalls may occur due to solar heating of rock surfaces, which
can cause outward expansion. Here we use data from 3.5 years
of field monitoring of an exfoliating granite cliff in Yosemite
National Park in California, USA, to assess the magnitude and
temporal pattern of thermally induced rock deformation. From
a thermodynamic analysis, we find that daily, seasonal and
annual temperature variations are sufficient to drive cyclic
and cumulative opening of fractures. Application of fracture
theory suggests that these changes can lead to further
fracture propagation and the consequent detachment of rock.
Our data indicate that the warmest times of the day and year
are particularly conducive to triggering rockfalls, and that
cyclic thermal forcing may enhance the efficacy of other,
more typical rockfall triggers.

It does beg the question though if it was 1000 years in the making, why Sept 2017?

It's hard to believe it's a coincidence that Pete's Junk show was hauled through that rock scar the day before it cut loose! Jus sayin...
;)