  We present ALMA observations of 106 G-, K-, and M-type stars in the Upper
Scorpius OB Association hosting circumstellar disks. With these data, we
measure the 0.88 mm continuum and $^{12}$CO $J$ = 3$-$2 line fluxes of disks
around low-mass ($0.14-1.66$ $M_{\odot}$) stars at an age of 5-11 Myr. Of the
75 primordial disks in the sample, 53 are detected in the dust continuum and 26
in CO. Of the 31 disks classified as debris/evolved transitional disks, 5 are
detected in the continuum and none in CO. The lack of CO emission in
approximately half of the disks with detected continuum emission can be
explained if CO is optically thick but has a compact emitting area ($\lesssim
40$ au), or if the CO is heavily depleted by a factor of at least $\sim1000$
relative to interstellar medium abundances and is optically thin. The continuum
measurements are used to estimate the dust mass of the disks. We find a
correlation between disk dust mass and stellar host mass consistent with a
power-law relation of $M_{\mathrm{dust}}\propto M_*^{1.67\pm0.37}$. Disk dust
masses in Upper Sco are compared to those measured in the younger Taurus
star-forming region to constrain the evolution of disk dust mass. We find that
the difference in the mean of $\log(M_{\mathrm{dust}}/M_*)$ between Taurus and
Upper Sco is $0.64\pm0.09$, such that $M_{\mathrm{dust}}/M_*$ is lower in Upper
Sco by a factor of $\sim4.5$.
